* 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>