Improve logging setup - Logback/SLF4J instead of log4j?

[Cervator]

Currently with Terasology we use Logback/SLF4J for logging and control it and any "bridged" logging frameworks from a single logback config file. I noticed while reviewing #415 that we're still doing log4j things in DS. For consistency's sake (and the added power of the newer frameworks) we should probably look into switching over.

See Terasology's setup for further details and https://logback.qos.ch/

Extra consideration here: Does Android require any additional considerations?

[Avalancs]

Not sure what extras they provide, but there are 2 repos I found:
sl4j-android: https://github.com/nomis/slf4j-android
logback-android: https://github.com/tony19/logback-android

The first repo is just the SL4J abstraction: https://www.slf4j.org/android/
The second repo is sl4j + the modified logback library.

I'll try out the second one, make a PR and ask someone to test it on Android.