Museum and tool updates

[patudom]

This should 🤞 finalize the Museum Conservation project content.

I made a few general updates to the tool, @VanessaPhippsCfa, which would be good for you to review especially carefully, as I don't want to break anything more broadly:

• I updated the metadata.json file to include the cellulose data and renamed "Paint Pigments" to "Paint Pigments & Supplies." I wasn't sure if the "&" would cause a problem, but it did not on my system, so I left it in. Please edit if it might cause problems on other browsers that I haven't checked.
• I learned that "angstrom" written out does not have the little circle accent so I removed it.
• Having all the wavelength/energy units capitalized on the x-axis label looked weird to me, so I changed them all to lowercase. I wasn't sure which strings were labels vs. type names, so I ended up changing everything I could find to lowercase. This is the place I'm most worried I may have broken a more general thing, so please review that commit (1f1df47) carefully.
• I relabeled the x-axis slider tool (per team meeting this morning) from "Plot width" to "Wavelength Stretch." I think this is a benign change, but if there's anything I missed, please fix!