Worked on the pull notification backend.

Also, introduced a Jolokia id for uniquely identifying a agent within a JVM.
This can be used to create agent specific MBeans. However, the id will
change over restarts, so it is not so suitable for static configuration
scenarios. The notification pull backend e.g. will use this ID for creating
the MBean holding the notification store. The name of this Mbean is returned
during the register call. The ID is also available now from the version command.
Worked on the pull notification backend.

Also introduced a 'jolokia-id' which is unique for each deployed agent (its
contained in the ServerHandle). That way, multiple agent can live in the
same JVM.

Furthermore destroy() lifecycle method have been introduced for certain
request handling classes especially for making unit tests easier (since the
NotificatioHandler will finally register an MBean which must be unregistered
before the next unit test).