Blender Git Loki

Tool System: use tool type enum to access brushes

Previously the brush names were used which had the limit that:

- Brush names that were deleted wouldn't show up in the toolbar.
- Naming collisions between user defined brushes and existing tools
broke tool selection.

Now brushes are created as needed when tools are selected.

Note, vertex/weight paint combine tool and blend modes,
this should be split out into a separate enum.