contracts: binary kill switch implementation

contracts/kill_switch/base/BinaryKillSwitch.sol

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+pragma solidity 0.4.24;
+
+import "./KillSwitch.sol";
+import "./IssuesRegistry.sol";
+
+
+contract BinaryKillSwitch is KillSwitch {
+    bytes32 constant public SET_IGNORED_CONTRACTS_ROLE = keccak256("SET_IGNORED_CONTRACTS_ROLE");
+
+    mapping (address => bool) internal ignoredContracts;
+
+    event ContractIgnored(address _contract, bool ignored);
+
+    function setContractIgnore(address _contract, bool _ignored) external;
+
+    function isContractIgnored(address _contract) public view returns (bool) {
+        return ignoredContracts[_contract];
+    }
+
+    function isSeverityIgnored(address /*_contract*/, IssuesRegistry.Severity _severity) public view returns (bool) {
+        return _severity == IssuesRegistry.Severity.None;
+    }
+
+    function _setContractIgnore(address _contract, bool _ignored) internal {
+        ignoredContracts[_contract] = _ignored;
+        emit ContractIgnored(_contract, _ignored);
+    }
+}