Possible renaming of NoData & WithData contracts

Based on conversations in https://github.com/hyperledger/firefly-tokens-erc20-erc721/pull/60, it's been suggested to move away from the `NoData` and `WithData` nomenclature currently used for the contracts.

The current thinking is `NoData` should be removed, so the contracts names are just `ERC20` and `ERC721`, because they are minimum viable implementations of their respective contracts.

`WithData` could be changed to `ERC20FireFly` and `ERC721FireFly`, since these contain all of the extra "recommended" FireFly functionality like URI's and attached data. However, dropping `WithData` makes the difference between the contracts less obvious. Plus, the `FireFly` suffix makes it sounds as though they are supposed to be the contract of choice for using with FireFly

Start by reading the discussion in pull request #60 and compare the proposed ERC20, ERC721, ERC20FireFly, and ERC721FireFly names. The work is done when the maintainers agree on a naming scheme and its rationale, with the affected contract names identified for any follow-up changes.

Written by the indexing model from the issue text.