Minor changes to make them work on postgres

* added default value to user_id and item_type
* changed model validation for user_id/item_type
Merge branch 'report_feature-wip' into travis

Conflicts:
	db/migrate/20140121132816_add_post_type_to_post_report.rb
	db/migrate/20140422134627_change_user_id_type_to_integer.rb
	db/schema.rb