minor database updates

Upon initial setup/migration my schema.rb had the `null: false` options removed.  I guess my postgres (9.2.4) installation is slightly different.  Anyway, to obviate the issue for anyone else, I've listed them explicitly.

Submitting for review as PR because it has the potential to take the site down.  It shouldn't, as there's no indication that the NULL option has changed for any table, but as they were never explicitly specified, I can't know for a fact.