Implement system RPC calls & error codes

[amerameen]

Work on each of these system RPC calls one PR at a time. Check mark completed calls as completed.

Reference: https://github.com/w3f/PSPs/blob/master/PSPs/drafts/psp-6.md

Please include integration test with RPC call implementation

System RPC Calls

• accountNextIndex
• addReservedPeer
• localListenAddresses
• localPeerId
• removeReservedPeer
• syncState

[edwardmack]

Questions:

• system_addReserverPeer/ system_removeReservedPeer, are we currently storing this info? Need understanding where I would add/remove these.
• system_accountNextIndex - nonce for given account, where would I find this?
• chain related data, seems to come from genesis definition, but our current test chain doesn't contain this, so need to research/test how we're going to handle these things (system_chain, system_properties)
  Defined in https://polkadot.js.org/api/substrate/rpc.html#system:
• system_chainType - I don't know what that is.
• localListenAddresses
• localPeerId