Ok.  I created this method in this service class so we'd have a generic way to get a count of articles in a category.  However, after I created it I realized that we need to join to the video_info table for this ticket.  This service has no business connecting to the video_info table and it would be really awkward for it to do so.

I've left this method in since it may be useful to someone else in the future.  I created another method in the VPT extension to get the count in the same place where we query category data there.

If we decide our special case should be in a service, we should probably move all category methods into a service in the 'include/' directory and out of the VPT and CategoryExhibition extensions.