Implemented site isolation

Added feature to isolate (lock) assigned sites: When you are in
a container with site isolation enabled, navigating to a site
outside of the assignments will open that site in a new default
container tab.

Co-authored-by: Francis McKenzie <francis.mckenzie@gmail.com>

src/js/background/messageHandler.js

@@ -32,6 +32,9 @@ const messageHandler = {
       case "neverAsk":
         assignManager._neverAsk(m);
         break;
+      case "addRemoveSiteIsolation":
+        response = backgroundLogic.addRemoveSiteIsolation(m.cookieStoreId);
+        break;
       case "getAssignment":
         response = browser.tabs.get(m.tabId).then((tab) => {
           return assignManager._getAssignment(tab);