Move everything inside app folder
Summary:
Do things like every other android app
Also, updated Android Gradle plugin version, raising min version of Gradle to 7.4
Test Plan: Check it builds correctly
Reviewers: valerio.bozzolan
Reviewed By: valerio.bozzolan
Subscribers: valerio.bozzolan, Libre BusTO
Tags: Libre BusTO
Differential Revision: https://gitpull.it/D111