Added BaseTween.
Generated engine schema clases.
Added BaseTweenCreator and TimeLineCreator.
Adjusted engine core tween-related clases to use the new system.
Added Timeline example to the CoolDemo "Welcome" label.
Auto generated engine schema javadocs.
Minor timeline creator bugfix.
Bugfix and Undo/Redo
Merge pull request #429 from anserran/master

Bugfix and Undo/Redo
Removed creators parameter from BaseTweenCreator#create method.
Improved Welcome label interpolation in CoolDemo.
Improved TimelineCreator for iteration.
Merge pull request #428 from RotaruDan/tweenTracks

Tween timelines.
Added selection array to the model.
Merge pull request #431 from RotaruDan/selectionList

Added selection array to the model.
Transparent clear color in abstract widget test
Modifier refactored: divided into grouper and handles
Renamed DragAndDrop to GroupEditor; extracted drag listener
Updated tests
Small bug fixes