Added Eigen linear algebra library.
Modified the library to use Eigen instead of in-house linear math library.
Removed the old in-house vector library.
Switched the in-house version of the XML library with pugixml.
Added a convenience header for accessing Eigen functionality from implemented components.
Added the graphics math class and implemented the world-to-screen helper function.
Added (somewhat hacky) macros to access engine systems from implemented components.
Modified the test components to use the new math library and access macros.