Allow setting the first screen to show on app startup
Summary:
Restore view state by hand after changing fragment (Android framework should be doing this automatically, but it doesn't)
Allow setting the first screen to open
Test Plan: Check it builds and that the changes are good (no crashes)
Reviewers: valerio.bozzolan
Reviewed By: valerio.bozzolan
Subscribers: valerio.bozzolan, Libre BusTO
Tags: Libre BusTO
Differential Revision: https://gitpull.it/D88