fatal: eXist killed by wrapper during startup/shutdown

Java service wrapper kills eXist if it takes too long to start up or shut down, resulting in fatal errors and potential data loss. Broker pool used to send signals to the wrapper to keep it waiting, but recently this failed due to broker pool being synchronized during startup. Solution: implement Observable on StatusReporter, which runs in a separate thread and is not subject to broker pool locks. Make it notify observers every 500ms.