Improve notification list view
Summary:
- Provide a filter to show just unread notifications.
- Visually show which notifications are unread.
- Style tweaks to make notifications more readable.
Test Plan: {F13494}
Reviewers: btrahan, jungejason
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D2883