Cat seeds!

Added real live cat photos to the seed file so users can see cool posts when they run 'rake db:seed'
We should be able to run the `rake db:seed` method multiple times, and only create these records once. Instead of using the `.create` method, use the `.find_or_create_by` or the `.find_or_initialize_by` methods. http://guides.rubyonrails.org/active_record_querying.html#find-or-build-a-new-object