Blender Git Loki

UI: Re-organize Brush Properties

- Consolidate each brush section (Color, Palette, Gradient) and make them distinct
- Remove the lock icons and move these items into an Options sub-panel, together with other toggles
- They now have more descriptive names
- Use an enum for view vs scene brush unit
- Use Property Split layout and sub-panels in line with the rest of 2.8
- Rename Curve panel to Falloff

Reviewed by: campbellbarton, pablovazquez

Maniphest Tasks: D4529

Differential Revision: https://developer.blender.org/D4529