NIRSpec IFU Demo Notebook (NEW TEMPLATE) (#29)

* added IFU demo

* PEP8 style fix

* Updates and techinical review

* Updated to correct some PEP8 issues

* Updated notebook to handle background observations

* Fixing remaining PEP8 issues

* Another PEP8 issue

* One more PEP8 bug

* review edits

* some PEP8 style fixes

* Fixed PEP8 issues

* removed function by mistake

* Trying to fix remaining PEP8 issues

* applied request from Law, extrat_1xd catch permission issues, updated 1.17.1

* Corrected PEP8 style  issue

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Co-authored-by: Rosa Diaz <rdiaz@stsci.edu>
Co-authored-by: David Law <dlaw@stsci.edu>