Animate Scrolling as Focus Moves on Overlay

[severinrudie]

Split out from #1312
Blocked by #1664

Requirements

• When no page has been navigated to (e.g., after clearing data), overlay should be attached
  • The top portion of the overlay (containing the toolbar) and the bottom (containing Pocket and pinned tiles) are visually attached, with no space between them.

* When a page has been navigated to and focus is on a toolbar element, the overlay should be split * The bottom portion of the overlay should rest low, near the bottom of the screen.

* When the overlay is split and focus moves down from the toolbar, the bottom portion will animate up. * This bottom portion will now cover most of the screen * As the user scrolls, the bottom portion of the overlay will act like a standard RecyclerView (i.e., the wrapper will not move, but content will scroll)