Improved ERC721 granularity (#1304)

* Split enumerable and metadata implementations.

* Renamed ERC721Basic to ERC721, and ERC721 to ERC721Full.

* Fixed linter errors.

contracts/mocks/ERC721FullMock.sol

@@ -0,0 +1,30 @@
+pragma solidity ^0.4.24;
+
+import "../token/ERC721/ERC721Full.sol";
+import "../token/ERC721/ERC721Mintable.sol";
+import "../token/ERC721/ERC721Burnable.sol";
+
+
+/**
+ * @title ERC721Mock
+ * This mock just provides a public mint and burn functions for testing purposes,
+ * and a public setter for metadata URI
+ */
+contract ERC721FullMock is ERC721Full, ERC721Mintable, ERC721Burnable {
+  constructor(string name, string symbol) public
+    ERC721Mintable()
+    ERC721Full(name, symbol)
+  {}
+
+  function exists(uint256 tokenId) public view returns (bool) {
+    return _exists(tokenId);
+  }
+
+  function setTokenURI(uint256 tokenId, string uri) public {
+    _setTokenURI(tokenId, uri);
+  }
+
+  function removeTokenFrom(address from, uint256 tokenId) public {
+    _removeTokenFrom(from, tokenId);
+  }
+}