Code style/Ops: use Logger.log instead of System.out.print[ln]

[bencomp]

Following up on #775.

java.util.logging.Logger provides a consistent way of sending log messages to the centralised log, including a level indicating the importance of the message. System.out.print and System.out.println messages do end up in the log, but without a source and all at Level.INFO.

It helps tremendously to operate a Dataverse installation if log messages are informative. That, to us, means that every message has at least a source and the right importance level. Currently there are nearly 200 uses of System.out in the codebase, although a lot are commented out and some are even "hidden" inside something like:

private void msg(String s){
    System.out.println(s);
}

The style guide has more tips for logging, like using the warning (or severe) level when an exception is caught.

[pdurbin]

I implemented this in 6535d9d and am closing this issue in favor of #3418.

[bencomp]

Nice work on the style guide, @pdurbin!

Note that println is still used – and not only in tests or command-line interfaces.