Blender Git Loki

UI: Consolidate masking-related brush controls

In the brush properties, some masking-related controls are currently available as a sub-panel in the Options panel, while others are in the Mask panel. I want to generally lessen the amount of controls in generic 'options' panels, since it's non-descriptive and rather a rather random grab bag of various controls. Better to group things in terms of their functionality with descriptive names.

This change consolidates the masking-related controls under one panel.

Differential Revision: https://developer.blender.org/D6577

Reviewers: Pablo Dobarro, Julien Kaspar