Add support for multiple chains on the website

[AnomalRoil]

Since we are now running v1.4 on Mainnet and we've planned to deploy a new chain in February, it would be nice if the website could support it.

Also we have an upcoming v1 of https://github.com/drand/drand-client that is moving away from WASM and using native TS for verification and that supports multiple chains and all. cc @CluEleSsUK

Maybe we could have a dropdown to select the network and chain?

Also having #64 supported might be nice (not only on mobile, we could have a "Copy" button next to the beacon value I'd say.)