Retrieve colors from all channels for some of pulse-based PAD preprocessors

related to bob.rppg.base#15 (closed)

Looks like only the green color value was returned when computing mean color values in a masked area

This affects both PPGSecure and LiPulseExtraction Preprocessors

created branch 24-retrieve-colors-from-all-channels-for-some-of-pulse-based-pad-preprocessors

mentioned in merge request !70 (merged)

closed via merge request !70 (merged)

mentioned in commit c3c6328b