introduce DC_IMAP_MESSAGE_MOVED event and try harder to send out MDNs

src/events.rs

@@ -48,6 +48,12 @@ pub enum Event {
     #[strum(props(id = "104"))]
     ImapMessageDeleted(String),
 
+    /// Emitted when an IMAP message has been moved
+    ///
+    /// @return 0
+    #[strum(props(id = "105"))]
+    ImapMessageMoved(String),
+
     /// The library-user should write a warning string to the log.
     /// Passed to the callback given to dc_context_new().
     ///