work on maintaining correct state (current presentation in pod)

...utton/core/apps/presentationpod/PresentationPodsApp.scala

...ps/presentationpod/SetCurrentPresentationPubMsgHdlr.scala

...cala/org/bigbluebutton/core/models/PresentationPods.scala

.../bigbluebutton/modules/present/managers/PresentManager.as

.../bigbluebutton/modules/present/model/PresentationModel.as

...luebutton/modules/present/services/PresentationService.as

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