Added a new notebook for pnCCD absolute gain calculation.
Dear Karim,
I have added one additional notebook (in the play_ground/ directory) which will take care of fitting and calculates pnCCD absolute gain. This notebook should not be used with xfel_calibrate and instead it should be used interactively.
I put it in a separate branch because I didn't want it to have any interference with the other branch you're working on. I hope this is OK with you.
Thanks again. Cheers, Kiana