storage improvement

The command pattern has been implemented so that ClearURLs also works in private mode.
See also: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/sendMessage

core_js/message_handler.js

@@ -0,0 +1,24 @@
+/*jshint esversion: 6 */
+/*
+ * This script is responsible for the communication between background and content_scripts.
+ */
+
+/**
+ * [handleMessage description]
+ * @param  request      The message itself. This is a JSON-ifiable object.
+ * @param  sender       A runtime.MessageSender object representing the sender of the message.
+ * @param  sendResponse A function to call, at most once, to send a response to the message. The function takes a single argument, which may be any JSON-ifiable object. This argument is passed back to the message sender.
+ */
+function handleMessage(request, sender, sendResponse)
+{
+    var fn = window[request.function];
+
+    if(typeof fn === "function")
+    {
+        var response = fn.apply(null, request.params);
+
+        sendResponse({response});
+    }
+}
+
+browser.runtime.onMessage.addListener(handleMessage);