Blender Git Loki

multiview: allow stereo display as a per window settings

That now means the D operator (stereo_toggle) can also be used to change
the stereo display settings of the current 'window'.

The 'toggle' part is currently not entirely functional because among
other things I still need to integrate the fullscreen editor operator in
the branch, so it can be integrated in this operator too.

This is advanced, but only advanced users should be needing multiple
displays to work in 3d (and those users can add their own shortcuts for
that, if we document it all well).

Same goes for pie-menus, we have approximately ten 3d modes, the mode
switch could very well fit in a pie-menu.

If a new file is loaded with 'Load UI' it will re-set the 'stereo
display' settings to the user preference ones. Otherwise it will keep
the windows to be whatever they were. So although the
wmWindow.stereo_display is saved in the file, it's never used.