Remove JNLP

[ghost]

Contributions and improvements are usually about making additions, but sometimes we need to remove things in order to move forward.

Marauroa has this dependency on jnlp.jar. It used to be part of JDK but has been removed and is not to be found in Maven repositories. I think it's actually non-free software.
This was also probably the main reason why the "mavenization" of Marauroa was not successful.
Since Stendhal is no longer using Java Web Start, I propose to remove jnlp.jar along with the WebstartPersistence class from Marauroa.
If we are concerned that other projects might still want it, we could extract a separate project, "marauroa-ws", which would only contain that class and would only depend on jnlp.jar.
Also we might want to do this in Marauroa 4.0, as doing it in 3.9.x would unexpectedly break the API.

Benefit: this would allow us to move to declarative dependency management, perhaps through Ivy at first, or directly through Maven.