Because the library still links to the old crappy opengl32.dll, we need
to load all symbols above OpenGL 1.1, not just those that are above
OpenGL ES 2.0/3.0.
Currently just regenerated the stock headers using flextGL, reducing
line count a bit. No dynamic extension loading or function pointers yet,
trying to make as little changes as possible.
The function pointer loading is now moved to Application classes to make
it possible to decide about platform-specific API at usage time, not at
library compilation time.
Currently it's not possible to create the Magnum context any other way
than through Application classes, will solve that in next commits.