Replace sout with Logging (SLF4J?)

[TinaTiel]

Didn't catch all the e.printstacktrace calls >.>

[TinaTiel]

A few things of note:

• I've set some reasonable defaults for the logging levels, including disabling Jetty logging.
• Default log level for the project is debug (see next points)
• Since this seems to be built around registering callbacks, what I've done is replaced direct error logging with calls to the respective runOnError, runOnConnectionFailed, etc. methods.

Inside those runOn... methods, I set it to DEBUG log the intended message so that the client knows something happened. I also include a debug message stating that no callback was registered, if relevant, so that they can know to register their own callbacks if they need to react to those kinds of events.