Need the ability to list ERC721 tokens for sale

[itsMarcoSolis]

As a seller
I need to have the ability to list any ERC721 token for sale
So that other users can see my listing and accept my offer.

Details and Assumptions

• To create a listing, the user must be registered.

Acceptance Criteria

Given the user has approved his token to be transferred by the Wyvern Proxy,
When the user lists an ERC720 item for sale and selects the desired ERC20 (If applicable)
Then listing must be added to the OrbitDB database, with the ability to be taken with both ETH or the specified ERC20.