Fixed Hero swapping

Got hero swapping working again. Noticed a bug, hero bullets will stop
updating and drawing once you switch from them to a different hero. Most
noticeable when shooting and switching rapidly between heroes.
Changes to NavMesh

Made some improvements (hopefully) to the nav mesh. I think this will
help simplify the pathfinding, and it's also a lot more efficient. I
also added zoom and rotation, mainly for debugging. Enemies will die
when the fall through the ground, though their physics stop updating
when they die.
First Iteration of Global Solver

Using a breadth first search to start out with. Currently it's only
drawn to the screen, not utilized by enemies. Added a current platform
property to all characters.
Merge pull request #35 from Lakon/master

dev merge