Enable changing or canceling stripe donations

[Pangalactic-GargleBlaster]

I needed to close the credit card account that the donations were coming from, so I needed to cancel the old recurring donation. To do this I had to bother the treasurer to find the credentials, log into stripe, find my donation and cancel it.
It would be nice to have a way to cancel or edit the recurring donations. The way I'm imagining this you'd write your email address in a form, the server would check if there are any payments under that address, send an verification email to that address and if confirmed it would cancel the donation or redirect to an edit page

[danasf]

I don't have the time to take on implementing right now but Stripe has a turn-key customer portal that allows subscribers to self-service their recurring charges.

Our form seems to be using an old version of their API and a deprecated Stripe JS component, so it may be worth considering a move to the Payment Element (or Checkout if we want a really low code option). This would require some back-end changes too, due to updates in the Stripe API (a move from Tokens->Charges to PaymentIntents).