* Add IERC721Metadata implementation into ERC721 * Add IERC721Enumerable into ERC721 * Update ERC721Pausable and ERC721Burnable * Delete ERC721Metadata, ERC721Enumerable and ERC721 (now ERC721) * Update mocks * Update tests * Update contracts/token/ERC721/ERC721.sol Co-Authored-By: Francisco Giordano <frangio.1@gmail.com> * Make ERC721Pausable and ERC721Burnable abstract Co-authored-by: Francisco Giordano <frangio.1@gmail.com>