Payments: migrate from Wise borderless-accounts to newer alternatives

[jayaddison]

We have a few references in the codebase to Wise Borderless Accounts; there are newer/preferred alternatives available in the Wise API for use instead.

If possible it'd be nice to rename some of our model database columns accordingly at the same time. I think we could do that by adding a second column of the same name / constraints, and performing an UPDATE during the upgrade/downgrade database migrations. Yes, theoretically an alias column would work too, but I think it may be simpler for the bidirectional migrations simply to duplicate the column temporarily.

An upgrade of the pywisetransfer dependency will be required alongside these changes.

[marksteward]

Probably worth waiting until after we wipe down the DB (should be in the next month), We can wipe all the migrations at the same time, as that's well overdue.