added on/off switch and expiration date on instanceKeys in sync

on/off is in settings.
when instanceKey date is 30 days old, it is deleted

fixed bug

src/js/background/messageHandler.js

@@ -10,6 +10,9 @@ const messageHandler = {
       let response;
 
       switch (m.method) {
+      case "resetSync":
+        response = sync.resetSync();
+        break;
       case "resetBookmarksContext":
         response = assignManager.resetBookmarksMenuItem();
         break;