added a scratchpad type element to the dialog so you can paint on the thumbnail.

A few other things:

1. scratchpad area can be disabled in case the person picks the existing thumbnail. I had to slightly modify the kis_scratchpad to achieve this.
2. Bringing in the current preset brush name
3. can clear the brush preview area.
4. the checkbox that lets you use the previous thumbnail now toggles on and off the UI elements and disables the ability to paint and clear