I modified entity to simlify parsing and added a placeholder for the Enemy class.  Also, Block was deprecated and removed, you should use platform instead of block from now on.  I also commited a sample parsing file (start.json).

Modified: Collisions, Content, Manager, Entity, and Player (May have messed up the player's size, but that can be fixed by changing values in the Player constructor).

Added: Platform, Enemy, and RoomData.

Removed: Block, Ball, and BallManager.
I just realized that I forgot to include the libraries that are needed for the project, so I am committing it again.