Fix initial loading of a route with an invalid session
Fix initial loading of a route with an invalid session

no issue
- if the session is "authenticated" but is invalid, the initial load of the app would fail. It could be replicated by:
	1. Authenticating in a running ghost instance
	2. Stopping ghost
	3. Deleting the database
	4. Re-starting ghost
	5. Closing the browser
	6. Re-opening the browser and visiting http://localhost:2368/ghost
- this fix stores the `transition` object for the duration of the initial load so that `sessionInvalidated` method can trigger actions before the transition has finished

dbalders/Ghost-Admin,TryGhost/Ghost-Admin,airycanon/Ghost-Admin,kevinansfield/Ghost-Admin,kevinansfield/Ghost-Admin,acburdine/Ghost-Admin,TryGhost/Ghost-Admin,dbalders/Ghost-Admin,JohnONolan/Ghost-Admin,airycanon/Ghost-Admin,acburdine/Ghost-Admin,JohnONolan/Ghost-Admin