Updated Level to use GameplayScreen's InputState for handling key presses

Signed-off-by: David Dorfman <wiz3kid@gmail.com>
Update README.md
Merge branch 'collision' into experimental
LevelScreen (renamed Level):
* Inherits from GameScreen.
* Now gets `AudioManager` from service.
* Now gets `ContentManager` from `Game.Content`.
* Removed player index from `HandleInput`, now uses `ControllingPlayer`.
* Renamed `InitTiles` to `Initialize` for consistency.
* Optimized collision.

Signed-off-by: David Dorfman <wiz3kid@gmail.com>
Merge branch 'my_last_master' into experimental