Bundle ERC721 extensions into base contract

contracts/mocks/ERC721BurnableMock.sol

@@ -3,6 +3,8 @@ pragma solidity ^0.6.0;
 import "../token/ERC721/ERC721Burnable.sol";
 
 contract ERC721BurnableMock is ERC721Burnable {
+    constructor(string memory name, string memory symbol) public ERC721(name, symbol) { }
+
     function mint(address to, uint256 tokenId) public {
         _mint(to, tokenId);
     }

contracts/mocks/ERC721GSNRecipientMock.sol

@@ -9,7 +9,11 @@ import "../GSN/GSNRecipientSignature.sol";
  * A simple ERC721 mock that has GSN support enabled
  */
 contract ERC721GSNRecipientMock is ERC721, GSNRecipient, GSNRecipientSignature {
-    constructor(address trustedSigner) public GSNRecipientSignature(trustedSigner) { }
+    constructor(string memory name, string memory symbol, address trustedSigner)
+        public
+        ERC721(name, symbol)
+        GSNRecipientSignature(trustedSigner)
+    { }
 
     function mint(uint256 tokenId) public {
         _mint(_msgSender(), tokenId);

contracts/mocks/ERC721Mock.sol

@@ -7,18 +7,36 @@ import "../token/ERC721/ERC721.sol";
  * This mock just provides a public safeMint, mint, and burn functions for testing purposes
  */
 contract ERC721Mock is ERC721 {
-    function safeMint(address to, uint256 tokenId) public {
-        _safeMint(to, tokenId);
+    constructor (string memory name, string memory symbol) public ERC721(name, symbol) { }
+
+    function exists(uint256 tokenId) public view returns (bool) {
+        return _exists(tokenId);
     }
 
-    function safeMint(address to, uint256 tokenId, bytes memory _data) public {
-        _safeMint(to, tokenId, _data);
+    function tokensOfOwner(address owner) public view returns (uint256[] memory) {
+        return _tokensOfOwner(owner);
+    }
+
+    function setTokenURI(uint256 tokenId, string memory uri) public {
+        _setTokenURI(tokenId, uri);
+    }
+
+    function setBaseURI(string memory baseURI) public {
+        _setBaseURI(baseURI);
     }
 
     function mint(address to, uint256 tokenId) public {
         _mint(to, tokenId);
     }
 
+    function safeMint(address to, uint256 tokenId) public {
+        _safeMint(to, tokenId);
+    }
+
+    function safeMint(address to, uint256 tokenId, bytes memory _data) public {
+        _safeMint(to, tokenId, _data);
+    }
+
     function burn(uint256 tokenId) public {
         _burn(tokenId);
     }

contracts/mocks/ERC721PausableMock.sol

@@ -7,6 +7,8 @@ import "../token/ERC721/ERC721Pausable.sol";
  * This mock just provides a public mint, burn and exists functions for testing purposes
  */
 contract ERC721PausableMock is ERC721Pausable {
+    constructor (string memory name, string memory symbol) public ERC721(name, symbol) { }
+
     function mint(address to, uint256 tokenId) public {
         super._mint(to, tokenId);
     }