No more statics in the engine
Changes in editor (just to avoid compilation errors)
Merge branch 'master' into enginerefactor

Conflicts:
	engine/core/src/main/java/es/eucm/ead/engine/actors/SceneElementActor.java
	engine/core/src/test/java/es/eucm/ead/engine/tests/GameControllerTest.java
Merge pull request #51 from anserran/enginerefactor

Engine refactor: no more statics in the engine