adapt Polls in akka-apps to work with the default presentation pod only

...bluebutton/core/apps/polls/GetCurrentPollReqMsgHdlr.scala

...bluebutton/core/apps/polls/ShowPollResultReqMsgHdlr.scala

...luebutton/core/apps/polls/StartCustomPollReqMsgHdlr.scala

...g/bigbluebutton/core/apps/polls/StartPollReqMsgHdlr.scala

...rg/bigbluebutton/core/apps/polls/StopPollReqMsgHdlr.scala

...g/bigbluebutton/core/apps/users/UserLeaveReqMsgHdlr.scala

.../src/main/scala/org/bigbluebutton/core/models/Polls.scala

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

...n/scala/org/bigbluebutton/core/running/MeetingActor.scala