Add notifications URL in Notifications panel

[bogas04]

I can understand how API might be limited in giving details of each notification, but as placeholder right now you can simply add a "Visit GitHub" URL that maps to https://github.com/notifications in the notifications panel so that one can easily jump to notifications.

[mbad0la]

@bogas04 the API has a notification endpoint.
I wasn't thorough with the payload at the time of this version and hence didn't implement it. I will be adding the notification detailing in future versions.