drawMappedEdges
- added DerivedMesh.convertToDispListMeshMapped function which converts and
also returns mapping information for use in editmode
- updated DispListMesh derivedmesh to be able to function in editmode
- update mirror modifier to support use as a cage
- update mirror & subsurf modifiers to properly pass mapping information down
modifier stack
It is now possible to have a mesh with mirror/subsurf modifiers where you
can edit with both as cage. Selecting the mirror'd part works, but of course
transform is flipped so it is a bit weird. Not the cleanest code in the
world and I can't say I am really happy with the architecture but it works for
now and supports the existing feature set.