New coordinate calculations for head penumbra filter

Corrects issues with coordinate system calculations for the head penumbra filter.    Head penumbra filter now works with multiple positional streams.   Filter initial cutoff frequency lowered to exaggerate the effect (will be tuned further over time).
To be clear, I was just saying to use qDebug() instead of printf() -- if we don't have that in our coding standard we should because we've previously made a point to clean up all printfs and convert them to qDebug. As far as making this a switchable option, you could add a new mixer option controllable from the domain settings page.