Fix room subtitle reloading

Replace the "reloadThis" ListModel hack by an actual signal,
works when the subtitle is displayed in more than one place
(e.g. two accounts in the same room connected).

harmonyqml/components/side_pane/RoomDelegate.qml

@@ -39,10 +39,18 @@ MouseArea {
                 rightPadding: leftPadding
             }
             Base.HLabel {
+                function get_text() {
+                    return SidePaneJS.get_last_room_event_text(room_id)
+                }
+
+                Connections {
+                    target: Backend.models.roomEvents.get(room_id)
+                    onChanged: subtitleLabel.text = subtitleLabel.get_text()
+                }
+
                 id: subtitleLabel
                 visible: text !== ""
-                text: Backend.models.roomEvents.get(room_id).reloadThis,
-                      SidePaneJS.get_last_room_event_text(room_id)
+                text: get_text()
                 textFormat: Text.StyledText
 
                 font.pixelSize: smallSize