Cleaner icons
Reduced the size of buttons and added new icon.
Added panel in scene edition with next options:
	Delete selected elements
	Move to back or front the selected elements
	Go to edit element
Adding more than one valid arguments in Action
Merge pull request #559 from angeldelblanco/action-bidimensional-validation

Adding more than one valid arguments in Action
Merge pull request #547 from anserran/newicons

Cleaner icons
name field added to repo element
Merge pull request #560 from jtorrente/repoelement-name

name field added to repo element
Adding an easy way to iterate through entities. Fixes #525
EngineLayers are added to the engine. Test updated
GameLoader updated to prevent layers getting removed unexpectedly
minor fix
New icons
Some strings
Avoid irrelevant enable events in actions
Bug fix in tab widget
Added WidgetUtils to encapsulate common methods to create widgets
Added MirrorSelection action
Added RotateSelection action
Added format tab to scene ribbon