Background added & some UI improvements/additions
- Added background and code related to that
- Created some prefabs (Player, UI, Background)
- Added PlayerMove.SetCeilToIntLastPositionZ() to get a ceil rounded int value of players position on Z axis
- Added Play.OnPressPlayAgain() and Play.OnPressMainMenu() to load the correct scenes when these buttons will be pressed
- Cleared Distance class from unrelated code
- Removed LosingPosition tag and added Ground and Background tags
Closes #3 (closed)