Update frontend build system to shed old dependencies, and address fallout from that

[jsdw]

This is mainly a pass just to bring things uptodate and try to be fairly standard in the libraries we use etc.

• move to Jest for testing
• new custom (but simple) Webpack 5 builds
• 2023 copyright headers
• remove various bits that don't appear to have been used for a while
• NPM instead of yarn

I've tested this locally and all seems to work. One thing that would be good to check is that the docker builds still work OK. I think they should be fine but want to be sure that you can still pass in the SUBSTRATE_TELEMETRY_URL properly for instance.

[jsdw]

Ok, so I built the docker image locally (with podman instaed of docker; nice that this worked seamlessly) and it seems to work ok now and the SUBSTRATE_TELEMETRY_URL env var is respected.