Blender Git Loki

Viewport smoke: add support for axis aligned slicing.

Current approach uses view aligned slicing to generate polygons for GL
texturing such that the generated polygons are always facing the view
plane. Now it is also possible to use object aligned slicing, which
creates polygons by slicing the object perpendicular to whichever axis
is facing the most the view plane. It is also possible to create a
single slice for inspecting the volume, or for 2D rendering effects.

Settings for this, along with a density multiplier setting, are to be
found in a newly added "Smoke Display Settings" panel in the smoke
domain properties tab.

Reviewers: plasmasolutions, gottfried

Differential Revision: https://developer.blender.org/D1733