Blender Git Loki

Support NURBS curve import & minimal groups support.

There's a problem though: the curve's vertices appear in edit mode
just fine, but the black line doesn't appear in object mode. But the code
so far should've been committed.

Also, some semantics have been made consistent which needed mesh
related functions/ members to be edited:
- `add_object_to_parent` for mesh is now similar to that of curves.
- `OB_MESH` is the default type of a raw object.

`copy_string_to_int` is also added to support multiple `int` values.