Implement proper logging

[fschlueter]

It would be a nice-to-have to implement a proper logging functionality. At least in the python backups that should be pretty straight forward.

[sjoerd-bouma]

Yes please! Or at least some way to make mattak SHUT UP. It's so talkative...

[cozzyd]

Yes this is a good idea, there are probably too many ad hoc printouts in various places/

[fschlueter]

But this is probably not going be possible without api breaks?