Use the same popover creation code in more places, which adds Escape and
Command-. to dismiss popovers.
Ensure that popovers both get and can accept first responder, preventing
keyboard input from leaking through to an underlying view controller.
Without this, it can be confusing as, for example, you can navigate to a
different story while you’ve got a ‘mark read’ popover shown for another
story.
Eliminated the old WYPopoverController from the code, since it isn’t
needed and isn’t compatible with theming. All popovers now use the
modern UIPopoverPresentationController mechanism.