Right now, app menu doorhangers/badges have their state managed
directly inside panelUI.js. This is problematic because these
doorhangers and badges usually have to do with Firefox itself,
and not the specific window that's showing them. Accordingly, the
simplest solution was to move panelUI.js's notification state out
into a jsm file, which will fire notifications that all panelUI
instances can listen to.
MozReview-Commit-ID: 7b8w1WsQ29p
