Image 404s on /docs/assays/*

[mccalluc]

• 4 404s on af
• 3 404s on atacseq
• 19 404s on codex
• 3 404s on imc
• lightsheet is still good!
• 1 404 on lcms
• 2 404s on maldi-ims
• 5 404s on mxif
• 6 404s on rnaseq
• 6 404s on seqfish
• 5 404s on pas
• 1 404 on wgs

[cebriggs7135]

We need a more stable host for the images. Stackedit does not store images. I've suggested that Melissa try https://imgbb.com to host the images, as recommended by Stackedit support.