Blender Git Loki

Assets: Add BPY function to mark and clear assets

Adds `mark_asset()` and `clear_asset()` to ID data-blocks, e.g.
`bpy.context.active_object.mark_asset()`. They essentially do the same as the
mark and clear asset operators.

Scripts are generally discouraged from using operators where possible, but we
need to provide API functions to use instead. In this case it means scripts
don't have to override context to pass an ID to the operator.