Replace usage of mesh.faces with mesh.polygons

- Check for keymap availability to suppress warning messages when running
  blender in background mode

indentation edits and copy pyrimid from contrib (where I had made some edits), removed so this wont happen again.

The fracture object was always created on layer 1 only (when this layer is not visible, ops.object.editmode_toggle hence failed). Now creating the fracture objects on current active layer(s).

Plus a few styling enhancements.

[[Split portion of a mixed commit.]]

- remove/comment unused variables
- remove unused imports
- fixed some bugs using incorrect variables

*Commented out non-manifold check on returned shards, it prevented open meshes to be fractured (e.g. Suzanne).
*Enhanced UI of Fracture Group op.

Missed these changes in last patch commit, had to manually merge due to changes in Extensions SVN 1010-1012. 

Applying [#22844] Fix for Fracture Tools, by Markus K. (markus111)
http://projects.blender.org/tracker/index.php?func=detail&aid=22844&group_id=9&atid=127

Sorry for the inconvenient, thanks!

moved fracture/ to object_fracture/ so that appears near the other object_ scripts

* Fixed usage of "relative_path" in bpy.ops.wm.link_append()
* Added "fracture" name to all operators somewhere.

* https://projects.blender.org/tracker/index.php?func=detail&aid=21793&group_id=153&atid=467
* TODO: Better file/dir name(s)?
* TODO: Cleanup UI a bit.