Create NeochatRoomMember as a shim for RoomMember

The intention is that NeochatRoomMember can be created passed to QML and then be fully managed by it. It effectively just grabs the current RoomMember, calls the correct function then discards it so that we don't end up trying to access an already deleted state event.

src/eventhandler.h

@@ -53,25 +53,10 @@ public:
      */
     MessageComponentType::Type messageComponentType() const;
 
-    /**
-     * @brief Get the author of the event in context of the room.
-     *
-     * An empty Quotient::RoomMember will be returned if the EventHandler hasn't had
-     * the room or event initialised.
-     *
-     * @param isPending if the event is pending, i.e. has not been confirmed by
-     *                  the server.
-     *
-     * @return a Quotient::RoomMember object for the user.
-     *
-     * @sa Quotient::RoomMember
-     */
-    Quotient::RoomMember getAuthor(bool isPending = false) const;
-
     /**
      * @brief Get the display name of the event author.
      *
-     * This method is separate from getAuthor() and special in that it will return
+     * This method is special in that it will return
      * the old display name of the author if the current event is one that caused it
      * to change. This allows for scenarios where the UI wishes to notify that a
      * user's display name has changed and what it changed from.