Use java.util.logging for logging

We have no default logging mechanism. Currently part is done by System.out and an access log is made using a custom logger, if configured.

It would be nice to have a default way to do logging. Since we try to depend on as little libraries as possible, it makes sense to use `java.util.logging` for this purpose.

The work I see is setting up a logging configuration (probably configured from plugins.properties). Also a proper default (console?) logging configuration can be set up.