Moved variable to storage contract

Author: maxsam4

contracts/datastore/DataStoreProxy.sol

@@ -8,9 +8,6 @@ import "./DataStoreStorage.sol";
  */
 contract DataStoreProxy is DataStoreStorage, Proxy {
 
-    // Address of the current implementation
-    address internal __implementation;
-
     /**
     * @notice Constructor
     * @param _securityToken Address of the security token

contracts/datastore/DataStoreStorage.sol

@@ -3,6 +3,9 @@ pragma solidity ^0.5.0;
 import "../interfaces/ISecurityToken.sol";
 
 contract DataStoreStorage {
+    // Address of the current implementation
+    address internal __implementation;
+
     ISecurityToken public securityToken;
 
     mapping (bytes32 => uint256) internal uintData;