Blender Git Loki

Point submodules to main Blender repositories

Solves issue with `make update` which expects submodules to be relative
to the blender.git.

Seems that it is important to do `make update` first time after this change,
otherwise local .git/config will use "wrong" URLs. This means the easiest way
to get proper thing to work is:

- Clone repository
- Switch to the branch
- Only then run `make update`