Implement web frontend

[ferrouswheel]

Use https://github.com/ericbets/danby - or another browser/gRPC proxy, to build a web api that trivially interacts with active services.

Requires #1 to be completed.

[ferrouswheel]

Another option is https://github.com/improbable-eng/grpc-web

[ferrouswheel]

With the implementation of #5, we can instead just call jsonrpc directly from a browser js client.