Several cleanups to the buildsystem:
- Do better factoring of common libs between platforms.
- Add support to building on Windows.
- Remove Qt4 support.
- Re-sort file lists and add missing headers.
This should fix the GL loading errors that occur in some drivers due to
the use of deprecated functions by GLEW. Side benefits are more accurate
auto-completion (deprecated function and symbols don't exist) and faster
pointer loading (less entrypoints to load). In addition it removes an
external library depency, simplifying the build system a bit and
eliminating one set of binary libraries for Windows.
After adding FindGLEW.cmake to externals, the variable call for the GLEW include path needed to be revised.
Append flags on OSX, rather than overwrite them.
I realized that GCC_COMPILE_FLAGS was changed to CMAKE_CXX_FLAGS mistakenly, so both were changed to a more platform-independent name.