Allow paging for transactions-by-address queries

[sisou]

As @paberr recently discovered, the tree structure we use for the transaction store lends itself to efficiently request transactions with an offset.

This option should be added to the RPC API, and then to the relevant protocol message.

• [ ] offset in RPC get_transactions_by_address
• [ ] offset in protocol receipts message

The change to the message will be a protocol breaking change.

[paberr]

I think this is a duplicate of #2697