Allow changing log level without having to recompile or repackaging the JAR

[sleberknight]

Currently the Logback logging configuration is embedded in the shaded uber JAR, which means it is fixed and cannot be changed without rebuilding, or cracking open the JAR, changing it, and re-packaging. 🤮

It would be much better to have a default Logback configuration but allow for a custom (external) configuration to override, similar to how Dropwizard lets you do it.

[sleberknight]

I also want to be able to have it log to a file by default, perhaps with a rolling file appender limited to a few files.