Custom profiles in bevel allows the profile curve to be controlled by
manually placed control points. Orientation is regularized along
groups of edges, and the 'pipe case' is updated. This commit includes
many updates to comments and changed variable names as well.
A 'cutoff' vertex mesh method is added to bevel in addition to the
existing grid fill option for replacing vertices.
The UI of the bevel modifier and tool are updated and unified.
Also, a 'CurveProfile' widget is added to BKE for defining the profile
in the interface, which may be useful in other situations.
Many thanks to Howard, my mentor for this GSoC project.
Reviewers: howardt, campbellbarton
Differential Revision: https://developer.blender.org/D5516
