Improve logging / remove debug messages

[KlemenDEV]

There seem to be some logging messages that are printed. This one is printed especially often:

ModernDocking/docking-api/src/ModernDocking/floating/DockingOverlay.java

Line 391 in 3fa9a8c

System.out.println(dockableRegion);

This should probably be removed or put under some sort of parameter

[nroduit]

I would recommend using the sl4j facade to manage log levels and abstract the logger used.

For the tests, you can use the Simple package:

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-simple</artifactId>
      <scope>test</scope>
    </dependency>

[tlf30]

I personally use log4j. But any logger is alright. Just note that dependencies on loggers suck for apps that are not using a logger. For apps that use a logger, there are adapters from just about any logger to anything...