Additional arguments in AddTxRequest

[ineiti]

The API to AddTxRequest could be improved:

On the client side, byzcoin/api.go:

• Add an argument to automatically call WaitPropagation, but only wait for the block returned in AddTxResponse.Proof.Latest to be included in all nodes

In the AddTxRequest call, return also:

• the index of the transaction in the byzcoin.DataBody.TxResults
• the resulting StateChanges
• wait for propagation to other nodes, for calls from other languages that don't have WaitPropagation included

This is probably a duplicate of another issue, but I cannot find the original one :(

Related: #2216