Contains buttons for operators that are useful when developing for
Rigify.  For now, it's buttons that generate python code for recreating
selected armatures.

I have updated the rig type API to be a bit clearer based on my
interactions with Kfir from PitchiPoy.

I've also disabled the "delta" rig type, as it is very obscure and
mostly just confuses people.

This required changes to both the default human metarig and some of
the rig types.  This updates the naming scheme to match new
best-practices, as per the CGCookie Flexrig.

This makes it much easier for e.g. someone to branch Rigify for
custom purposes, since there won't be weird name conflicts.

Also changed from using __import__() for dynamic imports to using
importlib.import_module().  This simplifies the code and should
be more robust.

Finally, misc pep8 cleanups.

The biggest fixes relate to keeping ID data modification out of
draw methods.  This was breaking Rigify with the current API.

Secondary fix was to move widget meshes to match the bones, even
if the widget meshes already exist.  It's nice for when the user
is progressively tweaking the metarig.

When using default UI_UL_list, one should always spully a custom ID, else collision inside an area are quite likely...

- dont import *
- dont use builtin names for vars
- strip trailing white space

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

* You only have to do layout.prop if you want 1 property, no need for row then!
* Use col, row, sub as variable names, not colsub, rowsub, row2 etc please.
* Povray Addon: Still used a lot of splits, you need no split when you only have 1 column! 

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

The layer names are then used in creating the custom rig layer UI.  This is
useful for users that do not want to--or do not have the knowledge to--edit
the generated python script by hand.  It is also handy even for more advanced
users when regerating the rig over and over (which over-writes the script
and any hand-made edits).

Also misc bug fixes in some of the rig types.

Clean-up of the IK/FK snapping code.  Should be much more maintainable now.

Also changed rig id generation.  Rig id's now consist of a random
alphanumeric string 8 characters long, with the smallest 8 digits of seconds
since the epoc (in hex) at the time of rig generation appended on the end.
This results in a 16-character string that is ludicrously unlikely to
have any collisions between rigs.  36^8 * 16^8, with the 16^8 being very well
distributed over time.  Ah... paranoia.

- Added IK/FK snapping (both directions) for legs.
- Cleaned up another operator so that it works with undo.
- PEP8 cleanups. 

Also cleaned up how some of the operators work.  They weren't playing nice
with undo.