created product to category relationship and edited controller and model file
refactored product and category models and relationship to make more DRY
fixed form for multiple selection box
Merge branch 'master' of github.com:lizrush/congo

Conflicts:
	db/migrate/20131216185523_add_columns_to_order.rb
	db/schema.rb
Merge pull request #23 from lizrush/product-to-categories

Product to categories