add more openzeppelin-solidity library contracts

contracts/mocks/MerkleProofWrapper.sol

@@ -0,0 +1,11 @@
+pragma solidity ^0.4.21;
+
+import { MerkleProof } from "../MerkleProof.sol";
+
+
+contract MerkleProofWrapper {
+
+  function verifyProof(bytes32[] _proof, bytes32 _root, bytes32 _leaf) public pure returns (bool) {
+    return MerkleProof.verifyProof(_proof, _root, _leaf);
+  }
+}