Consider implementing and hosting backend server / API

[cmoesel]

FSH Online is currently a client-side only app. It does not require any specific backend server (just a standard HTML server). This allows us to host it on GitHub Pages for free and with minimal maintenance. It also, however, prevents us from being able to implement some advanced features -- and requires creative solutions for things like the sharing feature.

These limitations would go away if we were able to implement and host a backend API -- so it's worth considering. After consideration, we may still decide that the current approach is still the best approach.