Blender Git Loki

Sculpt: New brush cursor, active vertex and normal radius

This commit includes the new brush cursor, active vertex updates and the normal radius brush property for all sculpt brushes.
-The new brush cursor previews the real stroke radius over the mesh and the sampled sculpt normal.
-The active vertex is used in sculpt tools and brushes as a starting point for an operation, similar to a preselection. It is also mirrored following the enabled symmetry options to preview the stroke symmetry.
-The normal radius brush property limits the radius that is going to be used to sample the sculpt normal and area center. It controls how closely the cursor follows the surface and it improves the behavior of most brushes, making them suitable for hard surface sculpting.

Reviewed By: campbellbarton, brecht

Differential Revision: https://developer.blender.org/D3594