Semtk & python3 Endpoint to unload and/or update owl

[cuddihyge]

Either the GUI or plug-in will eventually need to upload a new version of the owl (overlay).

Figure out the fine details of deleting. Delete prefix is probably too broad of a brush if when deleting an owl file that is referenced by another with something like a subclass relationship. Also want to get rid of blank nodes such as restrictions which can peskily hang around.