Add a status menu to the tray indicator

Reuses the existing StatusModel and combo box for most of the logic, and creates a new context menu allowing to quickly change the status without having to open up the main window.

I'm not sure what's the best way to detect a logged out account though, I searched through the account class and didn't see anything applicable. Changing the status while doing so is harmless (except for a log message saying that the auth object is empty) but ideally the menu should be hidden here.