Created and integrated ResourceManager

Resource manager created as a singleton class, it loads all necessary resources for current state according to information in resources.xml file and unloads them after leaving  current state. Added enum GameState to simplify work with states id. Created basic structure of resources.xml file.
Smooth camera rotation
Merge pull request #6 from alexanderguk/feature/resourcemanager

Feature/resourcemanager
Merge branch 'develop' into feature/collision-detection

Conflicts:
	src/core/GamePlayState.java
	src/core/model/gameplay/GameObjectMoving.java
	src/core/view/gameplay/GameObjectView.java
	src/core/view/gameplay/GamePlayView.java
	src/core/view/gameplay/HeroView.java
Margeded with Alex's resource manager feature branch