Non-Windows: Add empty stdafx.h

ep.c has to #include <stdafx.h> in order for precompiled headers to work on MSVC, add an empty stdafx.h so non-MSVC are happy
Mac: Add basic single-window app

Add basic single-window NSOpenGLView-based app targeting OS X 10.10.

This app:
- works correctly on retina
- correctly resizes with the window
- does not trigger GPU switch on multi-GPU MacBook Pros
- quits when window is closed

TODO:
- test what happens if GPU switches while app is running
- test moving from retina monitor to non-retina