API - Add Instance Count as Datasource Property

Wow @mnagel!  Thanks so much for this!  I'm going to look into running this so I can get that list put together.  I don't have any plans to systematically delete the datasources - I'm just wanting to compile a list so I can review them.  I'll feed the obvious ones into a script as a one-time purge and once I've done that, I can take a closer look at those that should be working, but aren't for whatever reason.