LP#2034617: improve how AngularJS handles logout BroadcastChannel messages

LP#2034617: improve how AngularJS handles logout BroadcastChannel messages

This patch reduces the risk that if there are multiple tabs of the
AngularJS staff client open, that logging out from one of them will
cause a storm of logout messages on the eg.auth BroadcastChannel.

If the open staff client tabs are all AngularJS, the result of that
storm can freeze the user's browser. However, if one or more of
the tabs are running the Angular client, the Angular tabs can
_also_ make repeated open-ils.auth.session.delete calls at a high
rate of speed, thereby degrading the availability of the
open-ils.auth service.

Testing involves opening up 4 or 5 tabs running the staff client, with
at least three or four of them running the AngularJS client. It
is strongly recommended that testing of this patch be done only on
personal, isolated test Evergreen systems.

Signed-off-by: Galen Charlton <gmc@equinoxOLI.org>
Signed-off-by: Jason Boyer <JBoyer@equinoxOLI.org>
Signed-off-by: Jeff Davis <jdavis@sitka.bclibraries.ca>