Blender Git Loki

Barebones for viewport code apart from 2.7x drawing code

A new option (set in the properties region) allows the user to pick the
"new viewport" for the rendering (in the UI: Modern Viewport).

For now we have a semi-blank file (view3d_draw.c) that can starts to take
over the drawing pipeline.

I can't guarantee we will be able to keep both drawing systems working
through the entire 2.8 development, but it should do for now.

also, we can use branches for some of the viewport development, but it's
better to keep things in 2.8 whenever we can, so people can test it.