script destinations.
This is mainly to support OP_RETURN outputs, which typically have a zero amount output value,
but as we don't special case OP_RETURN, this is currently done for all non-address scripts
Also, it's probably good to add a warning popup for OP_RETURN outputs with a non-zero output value, but this
would also need special casing for OP_RETURN.
Saving of script output payment identifiers is disabled for now, as reading the script from the stored invoice
back into human-readable form is currently not implemented, and currently only lightning invoices or address output
is supported.