Small refactors
Minor changes that fix some bugs and improvement the UI
Merge pull request #447 from RotaruDan/UI-improvements

UI improvements
Merge pull request #457 from anserran/smallrefactors

Small refactors
New assets for the skin
Added test to facilitate launching parts of the editor separately
Renamed ActorEntity to EngineEntity
Added an engine instance and a shape renderer to controller
GroupEditor: Added enteredgroupeidtion and endedgroupedition event
Some changes to make EditorUI work
Bug fix in ListCommand. forceCombine added to CompositeCommand
Added parent to Renderer Actor
Added EditorImageComponent and its processor
Added ModelActions to perform changes in groups edited in GroupEditor
Added tests for group commands
Added SceneEditor view
Added executable test for SceneEditor