Add Pagination to Notifications Settings Page

Problem to solve

Currently https://gitlab.com/profile/notifications this page is little bit laggy, I have 140 Project which takes little time to load, this might cause some performance issue to Database.

For those who have membership to even more projects and groups, it takes ~ 1 minute before the page loads:

Proposal

• Use Tabs to segment Project and Group notifications into their own lists
• Add Pagination via infinite scroll to the notifications settings page.
• Default to 40 Per page