create format model

I created a format model and added it to the story.tags method. Basically the same deal as the tones and topics. The only change I made to the FORMAT_NAMES list was to combine all the fundraising categories into one. I didn't make any attempt to change existing format names in the database to fit the new list -- should I?
this should match exactly what is currently at https://github.com/PRX/prx.org/blob/b54a61901f7a8560e9a6c5af6336dc001ad81e05/app/models/format.rb#L12