Cleanup the project hierarchy by moving and renaming some files

[Nitwix]

This is (was) a draft because:

• [x] Need to rename a few other things
• [x] Needs to be merged last so that it doesn't cause too many conflicts

Advice for reviewing this : look at this branch on android-studio, because the "Files changed" doesn't make the project hierarchy very clear.

[Nitwix]

I'm going to rebase on main, don't push please.