This PR is a ux change to make the header, tabbar, and post button disappear when the user scrolls.
The main tabbar is now an overlay which means it will display over views, this was needed in
order to get the timeline to extend behind it. However, this mean we must add bottom padding to any
view where the main tabbar is present to account for the overlap.
Changelog-Added: Disappearing header, tabbar, and post button on scroll
Signed-off-by: ericholguin <ericholguin@apache.org>
6751bc15cc