Improved movement logic, Property & Field cleanup

Replaced most Properties and Fields with Auto-Implemented Properties.
The program now checks to see if the keyboard state has changed before
re-calculating the movement vector.
Added ugly skybox
Replaced ugly skybox with less ugly skysphere
Better ContentManager

The ContentManager now utilizes dynamics, generic typing, and reflection
to greatly simplify resource loading. It can now also load Effects and
Textures in addition to Models.
Fixed ContentManager Bug

Fixed a bug causing the ContentManager to reload certain resources every
time they were fetched.