It's not obvious why this was ever a separate class name, since even
in c4219a4783 when it was first added,
it was styled identically to regular `fn` links.
This commit fixes a few inconsistencies and erratic behavior from the
notable traits, settings, and sidebar popups:
* It makes it so that pressing Escape closes the mobile sidebar.
This is a bit difficult to do on iPhone, but on other setups like
desktop tiling window managers, it's easy and makes sense.
* It makes sure that pressing escape while a notable trait popover is
open focuses the popover's toggle button, instead of leaving nothing
focused, since that makes more sense with keyboard navigation. Clicking
the settings, help, or sidebar buttons, however, will not focus the
notable trait popover toggle button.
* It ensures that notable trait and settings popovers are exclusive
with the mobile sidebar. Nothing should ever overlap a popover, and
there should never be more than one popover open at once.
