Improve player bottom sheet, in particular fling support

Fixes #101 #141

The current bottom sheet have usability problems. In particular, support of fling gesture is atrocious. This is an attempt to improve the situation using standard Google's Material BottomSheetBehavior. It also converts most of the layout to ConstraintLayout to lighten it up and uses databinding + ViewModel that is less error-prone than manually updating the views.

It also enables ladscape mode in AndroidManifest.xml because, weirdly some layouts for landscape did exists but the app was forced to portrait.

(Sorry for the size of the MR. It seems I'm unable to keep them them small )