Add optional marker to get_account_transactions

[LimpidCrypto]

The high-level method get_account_transactions should have an argument marker.
When requesting account_tx it is not guaranteed to receive all transactions an account has ever sent at once.
When an account has a transaction history that is too large, the node only sends a part of it, up to an amount it would become inefficient. If that's the case it also sends a marker field to indicate at what Ledger the node has stopped. The user can use it for the next call to tell the node where to start, to receive the next batch of transactions.

For get_account_transactions that argument is missing but would be very useful IMO.
If added to get_account_transactions, the function get_account_payment_transactions should also get that argument.

[JST5000]

Closing this as "won't fix" because it's better to just directly use the AccountTx request instead of building a helper which does the exact same thing without processing. In a version 2, we should probably remove the get_account_transactions sugar function since it doesn't add much to the raw request.