implement program parsing
implement sprite object parsing
implement user variable parsing
implement variables container parsing
Merge branch 'issue#84' of github.com:Catrobat/Catty into issue#84

* 'issue#84' of github.com:Catrobat/Catty:
  implement variables container parsing
  implement user variable parsing
  implement sprite object parsing
  implement program parsing
improve sprite object serialization and implement script serialization
remove all outdated toXML methods from data model classes