the biped leg rig.

- 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

involve any drivers.

Plus a few styling enhancements.

[[Split portion of a mixed commit.]]

* 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

This is the last piece that should allow some pretty extensive custom rigging
in the metarig, if advanced users choose to do so.

This allows advanced users to do certain limited custom rigging work
in the metarig, and have it transfer to the generated rig.
Custom properties are also copied when using the copy_bone function
in utils.
TODO: transfer drivers from the metarig as well.

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.

This allows IK arms and legs to still function properly even when they
start with an entirely straight chain.

This rig replaces the old spine rig, and has a super-set of the old spine's
features.  The main new features are:
1. A separate over-all control for translation.  Due to the pivot slide
   feature of the spine, it didn't really make sense to have one of the
   spine bones be the control for translation, so I broke that out
   into a separate control.  This control also acts as a root of the
   spine in general, including for scaling and rotation.  If you
   want to grab the entire spine as one unit, this is how to do it.
2. The spine can now have more than two control bones.  The rigger
   can specify an arbitrary number of the spine bones to be
   turned into controls upon rig generation.
   Controls that are not at the end points of the spine
   are optionally (via an animatable switch) auto-rotated by the
   the end point controls, so animators can ignore them when they
   do not require that level of control.

This is useful for bone chains that need their parent-child relationships
preserved exactly.  For example, bbone chains, and chains that users want to
use auto-ik on.
Also moved the 'copy' rig type to the basic collection.  This will break
some existing metarigs, but it is very easy to fix.  Just change the 'copy'
rig type on bones that use it to 'basic.copy'.

Matrix().Scale --> Matrix.Scale