[REQUEST] Get past transactions when subscribing to websocket service

[canguruhh]

When subscribing to the transactions of a set of addresses it would be great to add an optional parameter to ask the server to send the past transactions starting from a defined block height.

The command could be like this:

{"event": "subscribe", "channel": "tx", "address":["MJNo92g6DavpaCZbYjrH45iQ8eAKnLqmms"], "start": 1000000 }