Finished the alert (notification), fixed existing bugs

[Slice0w0]

Final alert is done by notifications, if not working, check System Preference > Notifications > Google Chrome (If still cannot see it popping up, restart Chrome and check the Notification Center)

Fixed bugs:

• prohibitedWebsites and visitedDomain are all undefined (so the .includes() always evaluates to true, i.e. every website visit generates an error message)
• Fixed the url/string type issue in setWebsites

Existing problem:

• notification message may not be able to fetch/decode correct local username from storage.local (error may occur on processing the Promise objects) but the default is set to User so the message should be reasonable (you can also simplify the message to get rid of it)
• try to do alert by sending alarm, but alarm listener is not working (alarm is sent correctly)