Blender Git Loki

Sculpt: brush input mappings improvements

Cleaned up brush channel input mappings:

* BrushMapping now stores .min/.max
* BrushMappingDef .min/max now sets BrushMapping min/max
instead of changing the curve preset bounds.
* Fixed how BKE_brush_channel_eval_mappings evaluates
the mappings stack. Mappings now blend directly
with channel value instead of accumulating a multiplier
that's applied at the end.
* Consequently, BrushMapping->blendmode now defaults to MA_BLEND_MULT.
* Exposed BrushMapping->blendmode in RNA and UI.
Note that it doesn't support every MA_BLEND_ type,
it provides its own EnumPropertyItem list of
supported blendmodes.
* Added a random input method, BRUSH_MAPPING_RANDOM.
* Fixed BRUSH_MAPPING_ANGLE being given data in the wrong
range (all channels should be 0..1, not -pi..pi).

Other changes:
* Improved the uv smooth brush. It's still hidden behind an
experimental pref.
* Added a SCULPT_temp_customlayer_has function to check if a temporary
customdata attribute layer exists.
* Fixed a bunch of broken sliders in the paint_toolsystem_common.py.