Blender Git Loki

Drivers Code Cleanups and UI Tweaks:
- Adding drivers from the UI (not from py-scripts though) will now
automatically add a "Transform Channel" driver variable to the newly
created drivers. This makes setting up drivers a bit more convenient
for the most commonly used case.

- Drivers now report their errors using the Reports system instead of
writing these directly to the console.

- Clarified some comments to be more insightful about the "why's" of
some design decisions, and related formatting/cleanup tweaks
- Reduced scope of "path" vars to just the scope they're required in

- Removed some unused defines from a failed experiment in the original
Keying Sets code ("templates" and "template flags") which was
superseeded by the more flexible + nicer "Builtin KeyingSets"