add initializableERC721

contracts/intf/IERC721Metadata.sol

@@ -0,0 +1,28 @@
+// This is a file copied from https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC721/extensions/IERC721Metadata.sol
+// SPDX-License-Identifier: MIT
+
+pragma solidity 0.6.9;
+
+import "./IERC721.sol";
+
+/**
+ * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
+ * @dev See https://eips.ethereum.org/EIPS/eip-721
+ */
+interface IERC721Metadata is IERC721 {
+
+    /**
+     * @dev Returns the token collection name.
+     */
+    function name() external view returns (string memory);
+
+    /**
+     * @dev Returns the token collection symbol.
+     */
+    function symbol() external view returns (string memory);
+
+    /**
+     * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
+     */
+    function tokenURI(uint256 tokenId) external view returns (string memory);
+}