On a contact page, show sub-agencies in the list of offices. 

This fixes: https://github.com/18F/foia-hub/issues/220

We used to show a list of offices. We didn't show a list of offices that we had designated as agencies (think FBI as a part of DOJ). We now have the sub-agencies show up in that list. 

This pull request also makes a number of PEP8 related changes that seem to have creeped in. 
Here is a new method and the crux of the change.