dialogs-instead-of-exceptions - The application should evoke dialogs instead of certain exceptions.

[todor]

The application evokes certain exceptions instead of dialog messages at the moment. The following changes should be done:

• Instead of throwing an exception when the server is already running a dialog with the following text should appear: One server instance is already running on this address.
• When opening other resource instead of image/text/book, instead of exception a dialog with this text should appear: The resource is not image/text/book.