Don't process form when discount code added

Ensure campaign_id is a proper integer.

Fixes: https://github.com/drastik/com.drastikbydesign.stripe/issues/92

ignore previous page no matter what the label is

validateForm update

Remove CC fields, then add them back to form after clearing associated rules in validateForm().

Revert removal of class assignment in buildForm, use QuickForm methods to apply.

Add form name for backend membership renewals.

Make civicrm stripe extension work with webform_civicrm.
Determine if stripe is really the intended payment processor.
Present "Edit CC Details" button if users "Go Back" in the submission process.

* Fall back to looking up the contact ID, apparent issue on Wordpress backend contribs.
* Catch error & display clear message when no email was found, instead of trying to query empty value.

Lookup contact's email address from API if missing from POST body (for backend contributions in Wordpress)

** This would cause the "Stripe.js token not passed!" because of a JS error.

Don't preventDefault on form unless stripe comes into play.
Include stripe-php extension.

Lots of code cleanup.

* Handle proper stashing of token for "Go Back" action on Contrib and Event forms.

Stash the Stripe token (including its value) from _Main form in _Confirm, in case they go backwards.

Revised JS logic