Update queryStakes JSONRPC method to support staking in different applications

[Tommytrg]

To support staking in myWitWallet and other libraries, the queryStakes JSONRPC method needs to support the following features:

• Include the nonce in the response to facilitate the unstaking process.
• Instead of returning only the total staked amount, queryStakes should return a map with two keys:
  • total: The total staked amount.
  • stakes: An array of stake objects filtered by the specified parameter (withdrawer, validator, or stakeKey).

To keep the JSONRPC and the CLI consistent, the changes should also be applied to the CLI method.

Issue related with witnet/my-wit-wallet#618.

[aesedepece]

  * `total`: The total staked amount.

The total might be irrelevant depending if we query by withdrawer, validator, or stakeKey. I'd leave it out and stick to just returning a vector of stake entries, with their corresponding keys, amounts and nonces. Calculating the total on the client side—when it makes sense—is trivial.