Blender Git Loki

Added options for how bevel amount is measured.
Now there is an 'Offset Type' dropdown on tool
shelf with types:
Offset - current method, offset of new edge
from old along sliding face
Width - width of new bevel face (if segments=1)
Depth - amount a chamfering plane moves down
from original edge
Percent - percent of way sliding edges move
along their adjacent edges

The different options mainly are useful when
beveling more than one edge at once.

Leaving as a TODO to put these in the modifier,
as doing that has more permanent effects so
want to let users shake out problems with this
first.