Feat/pn ccd

Dear Karim,

I have 3 notebooks for pnCCD flat-field analysis, two of which are not new but are considerably modified. One is new. I would like to merge them please. However, there are a bunch of things I'd like to discus with you before merging them. I will email those issues because they are rather long. Please read that email (I will send it today) before you start working on these notebooks.

Thanks very much and I appreciate your time and help. Stay healthy. Best Wishes, Kiana