Added voc-profile2 and changed edge threshold.

- Requires an experimental update of amitgroup, that let's you pass along
  unspread edges to code_parts.
- The parts' edge threshold is now expressed in average edges per pixel for
  unspread edges. This way it should not need to be changed (at least not
  nearly as much), if you change part size/frame and spread radius.
- Added a new temporary data set: voc-profile2.