Parenting mesh to bone

Moved from https://github.com/godotengine/godot/issues/772

From @EngjellRraklli:

> Parenting a mesh to a single bone of an armature in blender is not supported when exported in Godot,which means that the mesh doesen't move if the bone moves.


From @reduz:

> I'm not really sure how to export this properly with collada. Tried a few ways but didn't have much success. I will wait until the OpenGEX exporter works, and try again with that.

Start by reviewing the exporter code and its Blender armature and Collada handling; the issue does not name specific files or tests. Reproduce the reported case with a mesh parented to one bone, then determine whether the current Collada path can preserve that relationship. Done means the exported mesh follows the bone in Godot.

Written by the indexing model from the issue text.