Parse agora ad prep txs in Cashtab tx history
These are currently rendered as SLP SEND txs. They are SLP SEND txs, but a special case where we are sending to a p2sh script that is then immediately used to generate the offer.
We do not see the actual listing tx in Cashtab for SLP 1 agora listings, because we are not getting the tx history of the generated p2sh script. NBD, since in Cashtab we know this tx is always creating a listing.
Will see if can add offer details (price etc) in a reasonable way in a later diff. For now, at least parse correctly.
Note this also works for Agora Partials.