(no motor support or advanced settings yet)
added btStaticPlaneShape serialization
Added toggle in cmake for BenchmarksDemo to enable/disable graphics rendering
Note that BulletFileLoader is has no dependencies on BulletDynamics/BulletCollision.
Also added a custom build step to copy asset (.bullet and .obj file) into the executable folder
Made a few 'char*' 'const char*' to avoid compiler warnings