Missing contracts from Blockchain.Fae.Contracts

This module needs to be filled out with actually useful contract patterns; `sell` and `deposit` are good, `redeem` less so, `twoPartySwap` least of all (it is actually kind of obsolete, as the same activity can now be done at the meta-transactional level in a single transaction). Examples should be accumulated here.

- Factories: contracts that "manufacture" a return value, forever, in response to their arguments. The argument can only be a valuable if the contract is used as an escrow, but the return value might be. Example from the tutorial: [the `Nametag` factory](https://consensys.quip.com/9kkhA5IlabyD/Tutorial-3-Selling-buying-and-trading#CWNACAY8Tse).

- Token-locked deposits: the `deposit` contract is keyed to a particular signer, but there are situations where authentication by token is preferable (either alone or in combination with identity verification).