Add support for sudo

[dvc94ch]

@Dengjianping Do you want to finish it? Test is still failing because ensure_signed doesn't accept transactions with root origin. Closes #112

[Dengjianping]

Sorry for trying this so late.

I ran your sudo example as well as my own, I got error like this:

Rpc(Request(Error { code: ServerError(1010), message: "Invalid Transaction", data: Some(String("BadProof")) }))

It looks there's problem on the signer.

Update: I tried another test case test_tx_transfer_balance, got the same error. It's kind of weird.
rev: e7457b1eb9980596301fe1afd36478a6725157ef, 2020/5/07

[dvc94ch]

Have you tried purge-chain --dev?

[Dengjianping]

Yes, I purged the whole chain. By the way, current rev I'm using is kind of old, does older rev cause this problem? I see that subsxt is using rc2.

[dvc94ch]

@Dengjianping yes, that could definitely cause weird issues. I'm closing this PR for now.