Introduces a couple of prefs to control what gets logged, and removes some debug logs

I was getting a bit tired of scrolling through huge amounts of logs, so I introduced 2 prefs that can be toggled to decide which logs you want to see: toolbox <-> devtools and devtools <-> device.
Most of time I'm interested in seeing the devtools <-> device traffic, so I turned this one on by default.

@past @jryans @jlongster let me know if something like this is useful to you.