2.5: Painting

2.5: Painting

Various fixes for painting, sculpting and particle edit, still
much to be done...

* Move RNA paint and sculpt structs into rna_sculpt_paint.c,
* Added Particle Edit RNA.
* Some tweaks to existing Paint RNA.

* Put texture paint and particle edit object in context.

* Fix some errors in the brush layout, properly doing None
  checks, fixing some wrong property identifiers.
* Added tool enum for texture paint and particle edit in panels.

* Allow editing brush textures in the texture buttons, still with
  a stupid toggle, ideas for how to make the connection better are
  welcome.