GUAC-547: Add GuacamoleStatus object which enumerates all possible status codes, associating them with roughly-corresponding HTTP error codes.
GUAC-547: Associate a GuacamoleStatus with all GuacamoleExceptions.
GUAC-547: Define status for server exception - avoid future problems when generic error status changes.
GUAC-547: Implement exceptions for remaining status codes.
GUAC-547: Send status code as header. Use status code wherever GuacamoleExceptions are handled.