Distinguish log output from 'interactive' feedback in CLI

[orpheuslummis]

As pointed out by John on #389 (comment)

Several implementation ideas related to this:

• extend our internal logger interface with log.Print
• helper func in cli to handle the special requirement

Some goals:

• avoid double outputs
• always machine readable and equally-as-easily-handable as log output
• avoid repetitive code

[fredcarle]

Thinking about this a little more, we could keep track of where the logs are sent. If they are sent to the console, then there is nothing else to send as the dev will see the logs anyways. However, if the logs are sent somewhere else, then we could send human friendly messages to the console. That would mean that the solution would involve some modification of the internal logger.