Expire bundle changes that haven't been finished in 2 weeks
User story
I'm a user that wants to upgrade/downgrade my current subscription. I click on 'Manage Subscription' link in my profile page and follow the instructions to upgrade/downgrade but then I decide that I don't want to do the upgrade/downgrade.
If later I decide to do a different upgrade/downgrade I will need to contact support to deal with the change as the middleware does not allow me to cancel a upgrade/downgrade and these never expire.
Solution
Add new logic to process_bundle_changes()
so bundle changes older than 2 weeks won't be processed and the new order created for it is cancelled.
Add an button in 'Manage Subscription' page so the user can cancel the upgrade/downgrade if is still pending.
/cc @david.seaward