Notifications Dropdown infinite scrolling

I don't think there was an issue for this but i felt compelled to implement it after working on issue #5106.
Whenever the user scrolls to the bottom of the notifications dropdown it will load 5 more notifications until there are none left to show
This would reload all notifications. The notifications controller allows us to get additional notifications by using the `page` parameter. It would be great if you could use that. Perhaps write a new function (`this.getMoreNotifications`?) which calls `"/notifications?per_page=5&page="+page` where page is initially set to 3 and will be increased by 1 every time you scroll down in the notifications badge.