Implemented Behavior and SpriteRenderer components
added Camera support to Scenes
renamed Music asset to MusicTrack to be consistent with the core APIs.
removed type field from Asset class
renamed Texture class to Sprite and cleaned up references
Sprite class now has a field to determine if the sprite is a SpriteSheet (defaults to false)
Fixed references to MusicTrack caused by the rename in the last commit
renamed PanelRenderer class to SpriteRenderer and cleaned up references
cleaned up MusicSource in editor
Added TileMap and TileSheet classes
Changed Sprite.texture scope from private to protected