fix race conditions in the presentation and whiteboard startup

...src/org/bigbluebutton/main/events/PresenterStatusEvent.as

...uebutton/modules/present/ui/views/PresentationWindow.mxml

...uebutton/modules/whiteboard/managers/WhiteboardManager.as

...igbluebutton/modules/whiteboard/models/WhiteboardModel.as

...igbluebutton/modules/whiteboard/views/WhiteboardCanvas.as

...luebutton/modules/whiteboard/views/WhiteboardToolbar.mxml