Many changes: see description

Some Dependcies are setup:
  Tags get deleted if the User or Character or Photo gets deleted
  Photos have their poster set to nil if the poster account gets deleted
  Photos get deleted if their conventions get deleted

Adding con and searching forms now more specific.
  Though we now have a bit of a problem with the url box: it requires
http:// as a prefix

Convention now has validations.
  Can’t add or update a con without satisfying certain criteria.
Minor changes to how the year of a convention, and photos display.
  Year now could be xxxx-(xxxx+1) if relevant.
  Photos show who posted them.