Notifications UI
Notifications UI

Summary:
- Adding hover buttons
- showing timestamp
- adjusting colors

Reviewed By: passy, priteshrnandgaonkar

Differential Revision: D10461877

fbshipit-source-id: 1a384428ab2ce5d22a0e619055b04c1afdcbcb63

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper