NIRSpec MOS Demo Notebook (#28)

* added MOS demo

* updated requirements

* small fix for one of the plotting functions

* Technical review notebook and requirements file. Multiple changes.

* The notebooks changed name and moved to subdirectory. Removing

* Updated update_asn_paths function

* Pycode style fixes

* Update downloads

* edits based on review

* more review edits and PEP8 style edits

* Updated directory and associations

* Remove files from old mos directory

* MInor Chnages

* Remove unecessary cells

* Fix paths and file loop

* Fix asn print error

* filter 2D and 1D spectra by source_id for plotting

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Co-authored-by: Rosa Diaz <[email protected]>
Co-authored-by: David Law <[email protected]>