* Allow a client to create subscription periods, even if not
* authenticated

* Show a modal popup when a client selects the custom option in the list
* of interval delivery periods.
* If the option custom is selected the button add to cart is disabled.
Merge branch 'client_new_subscription' of github.com:mumoc/spree-subscribe into client_new_subscription

Conflicts:
	app/assets/javascripts/store/spree_subscribe.js
	app/assets/stylesheets/store/spree_subscribe.scss