Misc updates to the app
Summary:
Upgrade to androidx and raise minimum android version
Use worker for database update
Change source of arrival times
Test Plan: build, test and accept, and then make a new version for fdroid
Reviewers: valerio.bozzolan
Reviewed By: valerio.bozzolan
Subscribers: valerio.bozzolan, Libre BusTO
Tags: Libre BusTO
Differential Revision: https://gitpull.it/D45