Reinstate delegate calls (or something)

[nhynes]

One will notice that all calls are of the regular variety. Delegate calls are philosophically impure since every callee can inherit capabilities to the top-level caller. They're kind of useful, though, for keeping downstream code clean (e.g., for ERC20, the sender is always the account from which to transfer).

Ideally we'd just send caps individually, but this requires more thought. In the interim, we should just enable delegatecall (perhaps with a deprecation warning). Thank Ekiden for contract expiry 🙏