Fix BridgeMigration contract (#19)

* Fix wrong withdrawal's destination in BridgeMigration

* Add a function to give back the admin of PausableAdmin, fix pause/unpause function

contracts/v0.8/migration/BridgeMigration.sol

@@ -5,12 +5,6 @@ import "@openzeppelin/contracts/access/Ownable.sol";
 import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
 
 interface IGateway {
-  function paused() external returns (bool);
-
-  function pause() external;
-
-  function unpause() external;
-
   function withdrawTokenFor(
     uint256 _withdrawalId,
     address _user,
@@ -24,12 +18,26 @@ interface IGatewayV2 {
   function receiveEther() external payable;
 }
 
+interface IPausableAdmin {
+  function pauseGateway() external;
+
+  function unpauseGateway() external;
+
+  function changeAdmin(address _newAdmin) external;
+}
+
 contract BridgeMigration is Ownable {
   IGateway public gateway;
+  IPausableAdmin public pausableAdmin;
   address public weth;
 
-  constructor(IGateway _gateway, address _weth) {
+  constructor(
+    IGateway _gateway,
+    IPausableAdmin _pausableAdmin,
+    address _weth
+  ) {
     gateway = _gateway;
+    pausableAdmin = _pausableAdmin;
     weth = _weth;
   }
 
@@ -38,11 +46,15 @@ contract BridgeMigration is Ownable {
   receive() external payable {}
 
   function pauseGateway() external onlyOwner {
-    gateway.pause();
+    pausableAdmin.pauseGateway();
   }
 
   function unpauseGateway() external onlyOwner {
-    gateway.unpause();
+    pausableAdmin.unpauseGateway();
+  }
+
+  function changePausableAdmin(address _newAdmin) external onlyOwner {
+    pausableAdmin.changeAdmin(_newAdmin);
   }
 
   function migrateAndTransfer(
@@ -60,11 +72,11 @@ contract BridgeMigration is Ownable {
       "BridgeMigration: invalid array length"
     );
 
-    gateway.unpause();
+    pausableAdmin.pauseGateway();
     for (uint256 _i; _i < _withdrawalIds.length; _i++) {
-      gateway.withdrawTokenFor(_withdrawalIds[_i], msg.sender, _tokens[_i], _amounts[_i], _signatures[_i]);
+      gateway.withdrawTokenFor(_withdrawalIds[_i], address(this), _tokens[_i], _amounts[_i], _signatures[_i]);
     }
-    gateway.pause();
+    pausableAdmin.unpauseGateway();
 
     for (uint256 _i; _i < _tokens.length; _i++) {
       if (_tokens[_i] == weth) {