Blender Git Loki

Multiview Base Commit 7/10: Window Manager (to draw in stereo 3d)

This is part of the multiview rebase from a github to git.blender.org
repository. The rebase was made based on file areas, so build is likely
broken in some of those parts, but it bulds fine in the end.

The documentation and sample files were removed and now live in:
https://github.com/dfelinto/multiview-samples

The original git history can be found in:
https://github.com/dfelinto/blender/tree/multiview-pre-b3d

Code contributors of the original branch in github:
* Alexey Akishin
* Gabriel Caraballo

Original design made in contribution with Francesco Siddi
Original branch and design partially reviewed by Brecht Van Lommel