Add "Done" button when verification session is finished

It isn't immediately obvious when to close the window, other clients
(e.g. Element Web) has a "Got It" button in addition to the regular
dialog close button.

src/app/qml/KeyVerificationDialog.qml

@@ -171,7 +171,8 @@ Kirigami.Page {
                     return "";
                 }
             }
-            onDone: root.QQC2.Window.window.close()
+            isDone: root.session.state === KeyVerificationSession.DONE
+            onDone: root.closeDialog()
         }
     }
 

src/app/qml/VerificationMessage.qml

@@ -13,6 +13,9 @@ ColumnLayout {
 
     required property string icon
     required property string text
+    required property bool isDone
+
+    signal done
 
     anchors.fill: parent
 
@@ -32,6 +35,14 @@ ColumnLayout {
         horizontalAlignment: Text.AlignHCenter
         wrapMode: Text.Wrap
     }
+    QQC2.Button {
+        text: i18nc("@action:button Done, we are finished with verification", "Done")
+        visible: root.isDone
+        onClicked: root.done()
+
+        Layout.topMargin: Kirigami.Units.largeSpacing
+        Layout.alignment: Qt.AlignHCenter
+    }
     Item {
         Layout.fillHeight: true
     }