Move transactor implementations to "driver" implementations

[tyler-sommer]

Many apis offer integrations deeper than just processing credit cards. We should genericize the transactor implementations so we can more simply implement additional methods.

This might allow for simpler integration with "token creation" (which falls outside of processing a transaction many times, so integrating directly with a transactor is a bit strange)

[tyler-sommer]

This problem shows its face in NMI. The AchTransactor is different from the CardTransactor (though the former inherits from the latter) which causes a really wacky dependency chain.

Alternatively, an NMI adapter could be used that generically interacts with NMI, and then transactors become thin wrappers instead of the huge behemoths they are currently. Following, we could move validation to external classes, further separating concerns