CB Paid Subscriptions

Plan combination validity should be checked for upgrades to toggle client side plan required validity off as needed. Example scenario as follows.

Plan 1 (exclusive)
Plan 2 (exclusive)
Plan 3 (exclusive)
Plan 4 (non-exclusive)

User is subscribed to Plan 1. User wants to purchase Plan 4. User cannot due to the "required" class blocking form validation on plans 2 and 3. However their plan combination is valid as they've plan 1. In this case the required class should NOT be applied.