Show a notification instead of a login window on startup #3350

Show a notification instead of a login window on startup #3350

The original problem is that showing a popup not originated
from the main settings window while it's focused won't be
shown in front to the user.

This try not to highjack the user's attention of the user
by showing a notification when checking the connection for
valid credentials, and require the user to sign in through
the UI. There are still issues with showing that popup from
the tray icon, but the user will most likely be looking for
the popup in that case. The new sign in button directly in
the settings account works properly.