Consider upgrading to Bootstrap 5

[srabraham]

We're currently on Bootstrap 3 for the legacy IMS web app. Bootstrap 3 is way out of date at this point. Frankenstein suggests we consider a move to Bootstrap 5. This isn't a high priority thing, but I wouldn't mind learning Bootstrap 5 anyway, and IMS doesn't have all that many pages, so this might not be too difficult. I'll investigate a bit before going too deep.