Following on from https://github.com/metabrainz/acousticbrainz-server/pull/411

We should perform the following additional changes:

• Break each component up into a separate file
• If it makes sense, combine some components together - there are some very small components
• Switch from using jquery .ajax to fetch() to make queries (check if we need a polyfill)
• Remove uses of ts-ignore, any, and ! and replace with proper types
• change from using string constants to enums
• Set up react router so that each page has a proper URL, and set it up in flask as well
• Properly cancel fetch events when unloading a component (especially class view)
• reuse code between class-viewer and editor