Added OpenGL Mathematics (GLM) library that will be used in future OpenGL...

Added OpenGL Mathematics (GLM) library that will be used in future OpenGL code.  From the GLM description: "a header-only C++ mathematics library for graphics software based on the OpenGL Shading Language (GLSL) specifications. An extension system provides extended capabilities such as matrix transformations and quaternions."  It also contains functions that replace some of the GLU functions and some that replace OpenGL functions that are in the Fixed Pipeline OpenGL  API but not in the Programmable Pipeline OpenGL.  On Linux, the CMakeLists.txt file uses the PKG_CHECK_MODULES command to look for a GLM package and, if found, is used instead of the GLM headers in the Workbench source code.