Added ability to toggle the Popover

Added the ability to toggle the popover by clicking/touching the link used to invoke it, a second time.  This is useful for the case where a custom popover implementation doesn't leave much backdrop to click, hiding the popover...or when it is too far to travel for a click/touch.  Added mouse click handlers for showing/hiding to facilitate web use-cases, and simple rapid-click protection that could cause the popover to get "stuck" open, without the ability to close.