FOIA Portal Model

[morisy]

This will be a ways off, but thinking a bit more about the fields in #1209, I wonder if it makes sense to instead of saving a URL, create a FOIA Portal model.

I'm guessing the way it's going to work out is we have 7 or so different handlers that cover the vast majority of portals, but then each of those needs a separate instance for any given jurisdiction.

Complicating things, while some agencies will have their own portals others are going to be associated with entire jurisdictions. I'm not sure if jurisdictions should have links to portal or just assign every agency in the jurisdiction the portal, but Portals will be shared among some agencies, probably with slight tweaks in handling.