Create Router for RPC requests

[mpaulucci]

Ideally we would have a RPC router similar to the one describen in this video

https://www.youtube.com/watch?v=Gc5Nj5LJe1U

We should be able to do something like

   RpcRouter::new()
      .add("engine_exchangeCapabilities", engine::exchange_capabilities)

Ideally it would pass the rpc params field into the appropriate types to pass to the router function.

[lferrigno]

Blocked:

We need to define exactly which crate to use

[mpaulucci]

Closing for now, since it's low priority