importfeeds: add new 'echo' type that writes to stdout

After all, this seemed to be the most simple solution. I've looked at the embedart.py loggign code for writing to stdout.

Hmm; I'm not wild about overloading this parameter (what if someone wants to write a file called "stdout"? :smiley: Kidding aside, this makes the code harder to understand). Maybe we should not try to reuse `_write_m3u` and instead out your new logging loop right in `_record_items`.