Adds LinearGallery.
Adds SelectBox and LinearGallery to Transitionselector.
Fixes offset issues with Slice and Slide transitions.
Simplifies transitions names.
Merge pull request #913 from RotaruDan/transitionsImprovements

Transitions improvements
Outdated gdx version
Added new icons
Minor changes in skin, i18n, FieldName and SkinConstants.
Added ComponentIds class
Added DropdownPane widget .
Added minor changes in Switch and SceneElementContext.
Added action to edit timelines propierties.
Added methods to calculate duration and a sum of numerical propierties of timeline.
Added widget to edit animations_in.
Completed the EnterAnimationEditor.
Minor fixes
Removed ModelSelectBox and added TextField. Also removed the method doAction
Added minor improvements in BaseTweenDropdownPane.
Added listener to do the actions, and separate amount selectbox and speed selectbox
Added minor changes in some pads