Fix autocompletion

Now it will save a map from display name to id and use that to generate
clean matrix.to links. This also make sure the colors used for the
preview are correct by using NeoChatUser and fix the bug with the regex
by simply removing the regex.

Fix #234

src/actionshandler.h

@@ -70,7 +70,8 @@ public Q_SLOTS:
     ///
     /// This also interprets commands if any.
     void postMessage(const QString &text, const QString &attachementPath,
-        const QString &replyEventId, const QString &editEventId);
+        const QString &replyEventId, const QString &editEventId,
+        const QVariantMap usernames);
 
 private:
     Connection *m_connection = nullptr;