enhance Ditto java client with a "disconnection listener" * called whenever the connection to the Ditto backend was disconnected * provides a context of who initiated the disconnection + an optional cause * provides means to e.g. close the client as a result or to perform a reconnect
in addition: fixed executor service creation in Ditto: by default a ScheduledExecutorService with a high "corePoolSize" was configured as default * only use "scheduled" exector for schedluded tasks * provide Ditto client sessionId for thread factories (to append in thread names) * make it possible to configure user code provided "scheduled" executor
Signed-off-by: Thomas Jaeckle <thomas.jaeckle@bosch.io>