add cart validate
Merge branch 'master' of https://github.com/ipastushenko/depot

Conflicts:
	app/assets/stylesheets/carts.css.scss
	app/controllers/application_controller.rb
	app/controllers/carts_controller.rb
	app/controllers/line_items_controller.rb
	app/models/cart.rb
	app/views/carts/show.html.erb
	test/controllers/carts_controller_test.rb