Improvement: Update Stripe and Braintree gateways to "soft fail" after all essential actions have been taken. For example: if initial payment is successful but setting up the subscription fails, then registration is still deemed "successful" (whereas previously it would have been marked as a failure). In this case, membership is still activated but auto renew is disabled and a note is added to indicate the subscription creation failure.
Improvement: Add help next next to email reminders to clarify the difference between Expiration & Renewal reminders.
Fix: Convert stripe_checkout gateway to stripe in membership records.
Fix: RCP_Membership::enable() not enabling the membership. This caused a problem where memberships were not getting assigned when someone attempted to register, had their card declined, then tried again successfully.
