* on v4l screenshot, print out nosignal threshold values
* separate fractional parameters for no signal detection
* fully implement handling for "rainbow grabber"
* hyperion-v4l2 --screenshot can also evaluate best reagion and color for no signal detection
* tune output of no signal detection
* v4l outputs warninsg only, todo: make it adyustable
* typo
* v4l signal detection, now with validation checks
* remove obsolete schema files
* fix code style
* fix text typos
* code style