Dump OpenGL info earlier

This moves the OpenGL info dumping code into Graphics.cpp, which is probably the "wrong" place, but is where the OpenGL required-extension checks are done.

Also includes @fluffyfreak's change from #3137.

Adds code to check that GLEW was initialised correctly, and dumps out the list of supported compressed texture formats (code numbers only, unfortunately) as reported by `glGetIntegerv(GL_COMPRESSED_TEXTURE_FORMATS,...)`.