Incremental sync filters for API

It would be nice to filter by dates in the API to make incremental syncs.

1. Reservation changes. No updated_at (or updated_since) filter, so a cancellation, date change or financials adjustment on an old booking can only be caught by re-reading the whole check-in window. Ask: updated_at filter and sort[desc]=updated_at, same shape as booked_at.

2. Payouts and transactions. GET /payouts and GET /transactions take only page, per_page and include. Ask: start_date / end_date on the payout date, and ideally the same on /transactions.