Added two new types of buttons
Added TrackLayout, and adapted LinearLayout for extend it
Added test for TrackLayout and the new buttons
Adds some javadoc for DraggableScrollPane.
Merge pull request #674 from gorco/TweenTrack

Tween track
Merge pull request #681 from RotaruDan/draggableScrollPane

Adds some javadoc for DraggableScrollPane.