Error fixes for Structure.java

*Made changes in Game, Act, Scene classes (created setter method for act
and scene)
*Background is defined under Scene and not screen in the new
specification
-> Made changes in Structure class to reflect it.
*Commented out statements containing getter methods for name of Game,
Act, Scene, Screen in Structure class as they don't have name field in
the new specification
Renamed Background class to BackgroundType wrt to new spec
Merge remote-tracking branch 'origin/master'