MHX importer: Removed some dead code, and now display two digits for minor version number to avoid confusion.

Mhx importer. Rigs other than the mhx rig can now access the MHX Drivers panel. Drivers for facial shapes are located there.

Removed one additional reference to bpy.app.revision. I don't see errors caused by this variable because it is defined in all windows builds I have access to.

MHX importer: automatic helper deletion is temporarily turned off, because it often made Blender crash.

MHX importer: Added new convenient FK/IK buttons, which both change the IK property and layer visibility.

MHX importer: Multiple UV maps now work correctly with Bmesh. Added FK-IK snapping, stolen from Rigify.

MHX importer updated for BMesh. There are still problems with multiple UV maps, but am unsure whether this is my fault.

MHX importer: temporary commit for Bmesh. UV coordinates are ignored, but at least the script does not crash.

MHX importer: vertex groups can no be loaded in chunks. Also changed definition of helper geometry, to faces with material >= 4. This allows helpers to have different colors in the viewport.