Lutra should become more logger-friendly

Currently lutra mostly writes results and messages directly into streams and this is often done quite deep down in the system.

While not a problem for CLI-usage, this makes things difficult when using logging (e.g. on a server) and/or when console-output is not easily available. The mix-up between program output and technical output complicates things even more.

Lutra should separate program/user-centered output from technical output and become more logging-friendly.

A flexible approach could be to channel all output into one or more loggers and let logging configurations decide where to print what. This would keep the current convenience level for the CLI while enabling server-users to re-configure logging for their needs.