We no longer use offers for "I want to send you money", but we'll use
invoice_requests directly. Create a new table for them, and
associated functions.
The "localofferid" for "pay" and "sendpay" is now "localinvreqid".
This is an experimental-only option, so document the change under
experimental only.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-EXPERIMENTAL: JSON-RPC: `pay` and `sendpay` `localofferid` is now `localinvreqid`.
