Support for new ERC721 interface

- Tests for new features are pending
- ERC721 is abstract, since it requires metadata implementation
- Move some methods into DeprecatedERC721 contract
- Reorganise base vs full implementation
- Pending tokenByIndex

contracts/mocks/ERC721BasicTokenMock.sol

@@ -0,0 +1,17 @@
+pragma solidity ^0.4.18;
+
+import "../token/ERC721/ERC721BasicToken.sol";
+
+/**
+ * @title ERC721BasicTokenMock
+ * This mock just provides a public mint and burn functions for testing purposes
+ */
+contract ERC721BasicTokenMock is ERC721BasicToken {
+  function mint(address _to, uint256 _tokenId) public {
+    super.doMint(_to, _tokenId);
+  }
+
+  function burn(uint256 _tokenId) public {
+    super.doBurn(_tokenId);
+  }
+}