Blender Git Loki

Initial work to allow custom normals setting in BMesh, with quick bmesh py API call too.

Seems to be working OK from quick tests...

Some notes:
- This is mimicking BKE_mesh_evaluate code. While this is OK for some cases,
we'll likely want some more integrated and fine-grained ways to set/edit those
normals in Edit mode once we create real editing tools for those (most likely based
on some BMesh operators).
This implies some kind of dynamic caching/update of clnors spaces though, which
is not trivial. So kept for later, for now you have to set all custom normals at once.
- Not sure where/how to expose this in py API, for now just added a func in bmesh.utils.