Add pause sharing client event.

...utton/modules/screenshare/events/RequestToPauseSharing.as

...button/modules/screenshare/managers/ScreenshareManager.as

...ebutton/modules/screenshare/maps/ScreenshareEventMap.mxml

...gbluebutton/modules/screenshare/services/MessageSender.as

...button/modules/screenshare/services/ScreenshareService.as

...luebutton/modules/screenshare/services/red5/Connection.as

...screenshare/view/components/ScreensharePublishWindow.mxml