added example of emergency shutdown controller contract (#572)

oracle/esController.sol

@@ -0,0 +1,52 @@
+//SPDX-License-Identifier: GPL-3.0-only
+
+/*
+This contract can be used together with the emergency shutdown
+functionality of the TokenBridge oracles.
+*/
+
+pragma solidity 0.7.6;
+
+contract PauseController {
+    address public manager;
+    bool internal paused;
+    bytes32 private immutable ID;
+    
+    constructor (string memory _id, address _manager) {
+        require(bytes(_id).length <= 32);
+        bytes32 id;
+        assembly {
+            id := mload(add(_id, 32))
+        }
+        ID = id;
+        
+        manager = _manager;
+    }
+    
+    modifier onlyManager() {
+        require(msg.sender == manager);
+        _;
+    }
+    
+    function changeManager(address _newmanager) external onlyManager {
+        require(_newmanager != address(0));
+        manager = _newmanager;
+    }
+    
+    function pause() external onlyManager {
+        paused = true;
+    }
+
+    function play() external onlyManager {
+        paused = false;
+    }
+    
+    function isPaused() external view returns(bool) {
+        return paused;
+    }
+    
+    function id() external view returns(string memory) {
+        return string(abi.encodePacked(ID));
+    }
+    
+}