Review comments on Tezos API

[yaymukund]

The code was moving fast, and we may have missed updating some of them.

Specifically:

• The verifications were once meant to wait for the on chain state to update, but now we expect things to be correct at HEAD.
• The 'confirmation depth' code has changed.
• We changed the protocol so the customer waits for the merchant to perform a verification before funding the contract.
• Variable names may have changed.

[marsella]

See also: #335