Switch to vite for development

[oskarrough]

Do I really want this? I guess it is simpler.

• no longer have to use an 2-year outdated snowpack to generate ESM versions of the dependencies, because we can import from NPM
• can use a nice dev server from vite
• production build is optimized = faster to load (not that it was an issue previously of course)

Downside is that it won't run before vite has built it. But that discussion is getting old. If vite dies, any other bundler should do the trick.