Clip engine view
Simplified structure to relate EngineEntity and Actors

Now, instead of each EngineEntity having a group that has a child
which is the renderer, the renderer is directly associated to the
EngineEntity.
Added a default container in group editor

So panning/zoom isn't performed over the scene container directly,
which was provoking some side effects.
Tests fixed after changes
Refactor TouchListener
Merge pull request #620 from anserran/sceneedition

Some fixes in scene edition, along with clipping in the engine player