Improved implementation of foreground detection in frontend, added additional parameters

Average squared difference.   Average over all color planes.
Re-enabled blocked frame disabling
At startup of fectl, let it run with small time constant for a few seconds to quickly adapt
Fixed comment
Improved title layout
Support fg detector in checkcalibration
Improved noisedetect; made consistent with frontend
Added 'addpoints' option
Reduce min target size, increase window size