Add better support for custom logging

[latortuga]

The only easy way I could figure out to customize the logger was to monkeypatch Motion::Channel#log_helper method. There should be an easy config to set the logger.

[SlavaEremenko]

I second that proposal.

[gcentauri]

I talked with @alecdotninja about this at some point, though I don't recall the outcome. I'll see if I can refresh my memory today.