Fix logging implementation missing in CLI

[J-N-K]

Fixes #434

No logging implementation was included in the shaded jar resulting in the mentioned error message and missing log outputs.

[jstaerk]

@phax did we remove this on purpose?

[J-N-K]

It was never added. When switching from java.util-logging to slf4j you need to include the api and one of several implementations. slf4j-simple is quite common for standalone-cli-applications (it outputs to System.err), but you could also choose something like log4j or logback. That might require some configuration but also allows logging to a file.

[phax]

@jstaerk makes sense to me