Wrapper token

This token has deposit and withdraw functions to allow other tokens to be wrapped inside it.

This set-up is for use with 0x. Approvals are unlimited for the 0x proxy contract, and transferFrom can only be called by that contract.

• Deposit requires user to call approve on the original token, specifying the wrapper contract as the spender, before calling deposit
• Withdraw has a time lock, for a certain amount of time after the deposit, but can be released early if a signed hash is provided by Ethfinex