Adds a slider to solidify which allows the user to add bevel weight on the outside or remove bevel weight from the inside. Also includes a very small improvment for working with subsurface modifier where the rim edge in complex solidify will now also have a chance to get a crease if there is only two adjacent edges. Differential Revision: https://developer.blender.org/D7334 Reviewing and minor cleanups: Bastien Montagne (@mont29).