Automatic key import / export + Expected monad

Summary:
There are many things going on here (perhaps a bit much for a single patch):

- When an attachment is of mime type "application/pgp-keys", a button is added to import the key to GPG
- When sending a mail and crypto is enabled (encryption, signing or both), the public key of the first private key found is sent as an un-encrypted attachment (T6994)
- The `mailcrypto.{h,cpp}` was, for the most part, rewritten
- Introduction of the expected monad, inspired by what was proposed for C++ [here](https://isocpp.org/files/papers/n4015.pdf), but not at all a strict implementation of this specification. We may want to add some more features of this standard later.

The rationale for some of the choices:

- I found mailcrypto a bit hard to edit to add new features, and a great part was commented code to prepare for the support the SMIME crypto format, which would (in my current knowledge) not be used for sending emails.
- One thing I found that may be missing in the code base was a standardized way of handling errors in C++ code. Since exceptions are disabled I think that the functional way is the way to go. After some research I found the Expected monad / tagged union / sum type, which seemed to suit the problem particularly well.

In the long run, I hope we would move the entire code base to use `Expected` to indicate if a function might fail.

Of course every choice made here is to be considered as a proposition for doing things / RFC, critics wholeheartedly accepted.

Reviewers: cmollekopf

Tags: #kube

Maniphest Tasks: T6994, T8147, T6995

Differential Revision: https://phabricator.kde.org/D11158

5 files changed, 55 insertions, 0 deletions

diff --git a/icons/breeze/icons/actions/22/view-certificate-import-inverted.svg b/icons/breeze/icons/actions/22/view-certificate-import-inverted.svg
new file mode 100644
index 00000000..ff539ffc
--- /dev/null
+++ b/icons/breeze/icons/actions/22/view-certificate-import-inverted.svg
@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 22 22">
+  <defs id="defs3051">
+    <style type="text/css" id="current-color-scheme">
+      .ColorScheme-Text {
+        color:#f2f2f2;
+      }
+      </style>
+  </defs>
+ <path 
+    style="fill:currentColor;fill-opacity:1;stroke:none" 
+    d="M 3 5 L 3 17 L 13 17 L 13 16 L 4 16 L 4 6 L 18 6 L 18 11 L 19 11 L 19 5 L 3 5 z M 7.5 7 C 6.669 7 6 7.669 6 8.5 L 6 10 L 5 10 L 5 13 L 10 13 L 10 10 L 9 10 L 9 8.5 C 9 7.669 8.331 7 7.5 7 z M 7.5 8 C 7.777 8 8 8.223 8 8.5 L 8 10 L 7 10 L 7 8.5 C 7 8.223 7.223 8 7.5 8 z M 11 8 L 11 9 L 17 9 L 17 8 L 11 8 z M 11 10 L 11 11 L 16 11 L 16 10 L 11 10 z M 11 12 L 11 13 L 15 13 L 15 12 L 11 12 z M 17.5 12 L 14.707031 14.792969 L 14 15.5 L 14.707031 16.207031 L 17.5 19 L 18.207031 18.292969 L 15.914062 16 L 21 16 L 21 15 L 20.207031 15 L 15.914062 15 L 18.207031 12.707031 L 17.5 12 z "
+        class="ColorScheme-Text"
+    />  
+</svg>
diff --git a/icons/breeze/icons/actions/22/view-certificate-import.svg b/icons/breeze/icons/actions/22/view-certificate-import.svg
new file mode 100644
index 00000000..ec5250cc
--- /dev/null
+++ b/icons/breeze/icons/actions/22/view-certificate-import.svg
@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 22 22">
+  <defs id="defs3051">
+    <style type="text/css" id="current-color-scheme">
+      .ColorScheme-Text {
+        color:#4d4d4d;
+      }
+      </style>
+  </defs>
+ <path 
+    style="fill:currentColor;fill-opacity:1;stroke:none" 
+    d="M 3 5 L 3 17 L 13 17 L 13 16 L 4 16 L 4 6 L 18 6 L 18 11 L 19 11 L 19 5 L 3 5 z M 7.5 7 C 6.669 7 6 7.669 6 8.5 L 6 10 L 5 10 L 5 13 L 10 13 L 10 10 L 9 10 L 9 8.5 C 9 7.669 8.331 7 7.5 7 z M 7.5 8 C 7.777 8 8 8.223 8 8.5 L 8 10 L 7 10 L 7 8.5 C 7 8.223 7.223 8 7.5 8 z M 11 8 L 11 9 L 17 9 L 17 8 L 11 8 z M 11 10 L 11 11 L 16 11 L 16 10 L 11 10 z M 11 12 L 11 13 L 15 13 L 15 12 L 11 12 z M 17.5 12 L 14.707031 14.792969 L 14 15.5 L 14.707031 16.207031 L 17.5 19 L 18.207031 18.292969 L 15.914062 16 L 21 16 L 21 15 L 20.207031 15 L 15.914062 15 L 18.207031 12.707031 L 17.5 12 z "
+        class="ColorScheme-Text"
+    />  
+</svg>
diff --git a/icons/breeze/icons/actions/24/view-certificate-import-inverted.svg b/icons/breeze/icons/actions/24/view-certificate-import-inverted.svg
new file mode 100644
index 00000000..e0691d6d
--- /dev/null
+++ b/icons/breeze/icons/actions/24/view-certificate-import-inverted.svg
@@ -0,0 +1,13 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+  <defs id="defs3051">
+    <style type="text/css" id="current-color-scheme">
+      .ColorScheme-Text {
+        color:#f2f2f2;
+      }
+      </style>
+  </defs>
+ <path style="fill:currentColor;fill-opacity:1;stroke:none" 
+     d="M 4 6 L 4 18 L 14 18 L 14 17 L 5 17 L 5 7 L 19 7 L 19 12 L 20 12 L 20 6 L 4 6 z M 8.5 8 C 7.669 8 7 8.669 7 9.5 L 7 11 L 6 11 L 6 14 L 11 14 L 11 11 L 10 11 L 10 9.5 C 10 8.669 9.331 8 8.5 8 z M 8.5 9 C 8.777 9 9 9.223 9 9.5 L 9 11 L 8 11 L 8 9.5 C 8 9.223 8.223 9 8.5 9 z M 12 9 L 12 10 L 18 10 L 18 9 L 12 9 z M 12 11 L 12 12 L 17 12 L 17 11 L 12 11 z M 12 13 L 12 14 L 16 14 L 16 13 L 12 13 z M 18.5 13 L 15.707031 15.792969 L 15 16.5 L 15.707031 17.207031 L 18.5 20 L 19.207031 19.292969 L 16.914062 17 L 22 17 L 22 16 L 21.207031 16 L 16.914062 16 L 19.207031 13.707031 L 18.5 13 z "
+     class="ColorScheme-Text"
+     />
+</svg>
diff --git a/icons/breeze/icons/actions/24/view-certificate-import.svg b/icons/breeze/icons/actions/24/view-certificate-import.svg
new file mode 100644
index 00000000..f82c65b3
--- /dev/null
+++ b/icons/breeze/icons/actions/24/view-certificate-import.svg
@@ -0,0 +1,13 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+  <defs id="defs3051">
+    <style type="text/css" id="current-color-scheme">
+      .ColorScheme-Text {
+        color:#4d4d4d;
+      }
+      </style>
+  </defs>
+ <path style="fill:currentColor;fill-opacity:1;stroke:none" 
+     d="M 4 6 L 4 18 L 14 18 L 14 17 L 5 17 L 5 7 L 19 7 L 19 12 L 20 12 L 20 6 L 4 6 z M 8.5 8 C 7.669 8 7 8.669 7 9.5 L 7 11 L 6 11 L 6 14 L 11 14 L 11 11 L 10 11 L 10 9.5 C 10 8.669 9.331 8 8.5 8 z M 8.5 9 C 8.777 9 9 9.223 9 9.5 L 9 11 L 8 11 L 8 9.5 C 8 9.223 8.223 9 8.5 9 z M 12 9 L 12 10 L 18 10 L 18 9 L 12 9 z M 12 11 L 12 12 L 17 12 L 17 11 L 12 11 z M 12 13 L 12 14 L 16 14 L 16 13 L 12 13 z M 18.5 13 L 15.707031 15.792969 L 15 16.5 L 15.707031 17.207031 L 18.5 20 L 19.207031 19.292969 L 16.914062 17 L 22 17 L 22 16 L 21.207031 16 L 16.914062 16 L 19.207031 13.707031 L 18.5 13 z "
+     class="ColorScheme-Text"
+     />
+</svg>
diff --git a/icons/copybreeze.sh b/icons/copybreeze.sh
index b7c85229..5697b4b6 100755
--- a/icons/copybreeze.sh
+++ b/icons/copybreeze.sh
@@ -13,6 +13,7 @@ wantedIcons = [
     "document-decrypt.svg",
     "document-edit.svg",
     "document-encrypt.svg",
+    "view-certificate-import.svg",
     "document-save.svg",
     "document-sign.svg",
     "edit-delete.svg",