Moved some widgets to dragndrop package.
Removes Cell#ignore(), libGDX removed that method when forked TableLayout.
Adds DraggableLinearLayout, supports dragg'n drop via events.
FocusItemList supports selection via events.
Changes FramesTimeline to use the new FocusItemLIst features.
Changes AnimationEditor to use the new FocusItemList featues.
Small changes to AnimationEditorTest.
Comments addressed. Some typos, javadoc, etc.
Merge pull request #691 from RotaruDan/draggableLinearLayout

Draggable linear layout