made tag search dive into contact tags.

This makes it so that tags from contacts propogatae to the partner in PRM (but they aren't actually added to the partner). This also makes contact tags searchable in PRM, instead of just partner tags.
There isn't any noticable lag here, but I'm wondering if there is a cleaner way to traverse contacts? I'm thinking something to do with `select_related` in the view, but I'm not sure.