Remove checkout_states helper for Spree 1.3.x support. [Fix #120]
* Disable doesn't work for radio buttons
* After API refactoring the input items are not shown on document ready, therefor the even doesn't hide/disable them.
Fix: Do not redirect to paypal if there is an error on the Order model

In case there is a validation issue with the Spree::Order we do not
want to redirect to the paypal page but resolve the error.
Fix specs for Spree 2.0.x
Removed old refs to frontend and backend