Moved CheckBallTileIntersection() to PhysicsManager

-Moved CheckBallTileIntersection() to PhysicsManager. It returns a
share_ptr< Tile > which is nullptr if no intersection.
-Moved DidBulletHitTile() to PhysicsManager.
Cleaned up GameManager

-Improved output.
-Removed empty lines
-Moved physicsManager.Add to PhysicsManager itself
Added checking if file exists before loading level

-Added funcion CheckIfFileExists() and FindNextExistingBoard()
-FindNextExistingBoard() iteratates through the list of filenames in
boardlist. It will return the first fila path it finds or "" if the last
fiile was the last that existed.
-This fixes issue with empty Boards and prevents having to run
GenerateBoard() if the next line in boardList refers to a file that
doesn't exist
Fixed issue with new Board

-Boards can be different between two connected clients
-Chnaged it so that only server can decide it's time for a new Board in
twoplayer mode