Open the home pane if there are messages in other panes

When you had RiotX’s “direct messages” pane open, then close the app and get a message in a “room”, RiotX currently shows up with still the “direct messages” pane active when opened.

* I guess it makes sense to open RiotX with the home pane instead – at least when RiotX gets opened through tapping on a notification.
- When RiotX gets opened through the app icon, the current behavior might also be ok.
* If people only get messages from conversations of that last active pane, switching to the home screen makes not much sense.
* Older, unread messages should not influence that behavior, because these are already indicated via the bottom icon bar. And these might be unread in the first place, because the user seems wanting to handle those at a later point in time. So just incoming messages since RiotX’s last active usage should be considered for this behavior.