Refine Notebook page-switching pagination behavior

The first prototype of pagination in the Notebook executes a simple "scroll-to-top-of-view" animation when navigating between pages of results. Assess whether this can (and should) be improved before meeting the first Notebook milestone.

Some possibilities include:

* Briefly displaying a loading spinner to emulate a page load
* Tuning the animation timing
* Removing current results from view before "changing the page"

_Amendment_: Also, it was noted in the review of the pagination implementation that the handling of the removal/management of button `focus` when changing pages is likely in the wrong place. It may make more sense to have that owned by the parent/relevant component.