Save devices as InetAddress object

Previously it was stored as String
Add comment on usage of debug mode
Add AliveWatchdog

Listens for alive messages of devices and tells if new were found.
Fix IOException when device list is empty
Add listen_only property in case no devices were specified
Refactor AliveWatchdog
Create additional ControllerClass, out-source code from MainClass
Exit program after process -h or -v argument
Modify SimpleDatagrammSocket for general usage