Added check to OpenGame to ensure EditState has a editScene
Merge pull request #461 from anserran/editopen

Added check to OpenGame to ensure EditState has a editScene
Initialize, release and build timelines added to the tweens widget.
Adapted TweenButton and TweenDragButton in order to get initialized correctly.
Improved tween functionality code readability.
A first approach to a repository implementation.
ElementButton improvements.
Download, unzip and display the repository thumbnails.
Fixed Android skin loading path.
Added I18N strings.
Added selectable flag for BaseGallery.
Improved RepositoryGallery.
RepositoryGallery refactoring and javadocs. Now resources are fetched locally before downloading them.
Go to SceneEdition after clicking a repository element.
Fixed unused imports.
Improved RepositoryGallery javadocs.
Refactoring and javadocs. Resources are downloaded from the online repository and imported to the project.
Elements are now fetched in the local cache before trying to download them when importing.
Added javadocs.
Separated control from view in RepositoryGallery. Created RepositoryManager.
Added ImportElement action.