Appended collision code to 'Map' class

Changes:
Collisions use a custom class called: 'Circle2D'. As collision circles.
(XNA doesn't have a way to handle collisions between two round objects,
possibly because the algorithm is so simple)

Known Bugs:
The collisions work perfectly fine between two ships.. However if you
spawn more than two. The behaviour of all ships collisions go a bit
strange. This needs some debugging.