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.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@61221 954f8c5b-7b00-dc11-b283-0030488c597c