Standardize istanbul RPC Method Names

[trianglesphere]

Description

It appears that the geth management console takes different function names from the json RPC. These should ideally be standardized and documented.

Context

From Girish Nuli | CoreBlockchain on discord

// This works
sudo docker exec celo-fullnode geth attach --exec 'istanbul.replicaState'

// This does NOT work
curl <IP address>  -X POST --data '{"jsonrpc":"2.0","method":"istanbul_replicaState", "params":[], "id":1}' --header "Content-Type: application/json" 

// This works
curl <IP address>  -X POST --data '{"jsonrpc":"2.0","method":"istanbul_getCurrentReplicaState", "params":[], "id":1}' --header "Content-Type: application/json" 

[girishnuli]

For reference, list of all istanbul methods can be viewed at below link from line 741 onwards. Many of them need to be renamed or the docs updated for consistency.

https://github.com/celo-org/celo-blockchain/blob/6272484ac696770ba103b08244e62d07724dcbf6/internal/web3ext/web3ext.go