Major update

Implemented map loader both on client and server.
Multi-threaded server so now it can update and run a CLI for server
commands.
Added primitive serverside collision detection.
Added two basic test maps (Default.xml and Warzone.xml).
Integrated rapidxml library into the project.
Added 3 new art assets used by the maps.
Added ServerCommands.h which contains #define arguments used by the
server to identify input.