Subnet types

This includes two things:
1) replace the initial subnet types list with a fuller list, and related refactoring
2) the first iteration of the NetworkQuery API/helper class for grabbing interfaces, etc for hosts in the context of a particular subnet type.

1) is largely done here; 2) will need more work, but that could be done either as part of this PR, or as a follow-on PR after merging this one, since it's not referenced anywhere yet.
I'm not sure what's correct here, should we destroy records in seed? What if user does some manual assignment? On the other hand I see the benefit for devs.