get badpx due to bad gain separation

This MR has two features.

1. The ability to define an offset or noise threshold for each gain. The old parameter is left for back compatibility with old configurations and for the ability to give on threshold for all 3 gains.
2. Catching the bad pixel for bad gain separation depending on a gain_sigma which can be configured for the notebook.

Report sample for two modules: CharacterizeDarkImages.pdf

@jsztuk @karnem