Refactored Mesh class

Removed glm_vectors and glm_normals to speed up processing time and
reduce memory usage.
Refactored ShaderProgram class

Changed input parameters from const string & to const char *
for better speed and less memory usage.
Updated .obj mesh files
Renamed MulitipleObjects_Example

Renamed to FlatSmoothShading_Example
Modified FlatSmoothShading_Example

Added ability to move light along z direction with keys p and l.