Restart/Logging/Debug tweaks

[slominskir]

Watching log files and the web console after deploying version 1.17.0 revealed some issues:

• On restart DBR can be null so instead of sending empty string just forward null.
• There is a race condition in that javax.websocket.Session object will throw an Exception if you try to interrogate it after it is closed. This means on the debug screen if a client goes away right after the list of sessions is forwarded to the console and then the console calls methods on the session looking for ID, IP, User Agent, etc. then console crashes.
• Some log message log levels need adjusting and session ID info needs to be included
• Re-enable dropped message logging, but only log at thresholds to avoid flooding the log.