Pausing/Resuming, improved exception handling, connection check at startup

In the latest version of the AleHu client it is possible to pause the transmission/reception of messages.

Besides, an improved exception handling in case of connection problems should further improve the stability of the client.

And finally, a check at startup was added to test if connections to the AleHu server were possible. If connections fail, the user is advised to check the proxy settings in the properties file of the client.