Linux Build fixes

A set of fixes to improve cross platform compatibility
+  added GLEW sources 
+ Added cmake build script to glew sources - Glew is not that complex to compile.
+ Updated GLFW - The current version of GLFW features CMake support build options.
+ Fixed compile problems on Linux. 
+ added needed fixes for the above changes.
+ Added automatic download and use of updated khronos headers to prevent problems with compiling.
+ Some compile fixes ( [f4aebd3](https://github.com/kphillisjr/ogl-samples/commit/f4aebd3e29c3ef34a3d6827bc9e29b342e01205e) ) are meant to fix compile problems with 64-bit linux.

TODO:
+ Verify and Fix that Windows compatibility is still working fine.
+ Verify and Fix Mac OSX Compatibility - I cannot take care of this since I do not own a Mac.
+ Verify that all samples work as intended. There is some key changes to relevant to [Updating GLFW 2x to GLFW3](http://www.glfw.org/docs/3.0/moving.html)