implement program parsing
implement sprite object parsing
implement user variable parsing
implement variables container parsing
implement program serialization
implement sprite object serialization
implement user variable serialization
implement variables container serialization
implement user variable serialization
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remove all outdated toXML methods from data model classes
implement sound serialization
implement look serialization
implement script serialization
implement SetLookBrick serialization
set xmlElementWithContext method required in CBXMLNodeProtocol
implement PointToBrick serialization
implement PlaySoundBrick serialization
fix some serialization bugs