Sort rooms by last event, not unread count.

src/spectralroom.cpp

@@ -140,3 +140,8 @@ void SpectralRoom::sendReply(QString userId, QString eventId,
            "</blockquote></mx-reply>" + sendContent}};
   postJson("m.room.message", json);
 }
+
+QDateTime SpectralRoom::lastActiveTime() {
+    if (timelineSize() == 0) return QDateTime();
+    return messageEvents().rbegin()->get()->timestamp();
+}