RemoteExam now has a method logout to give the ExamClient a chance
to inform the RemoteExam that he logged out + it now holds
a ArrayList with ExamParticipants that are currently logged in.
src/java/de/fhworms/ztt/ox/deployment/LinuxExamDeploymentImpl.java
src/java/de/fhworms/ztt/ox/examserver/ExamAdministrationClientConnectorImpl.java
src/java/de/fhworms/ztt/ox/examserver/RemoteExam.java
