Accept a `null` value as response for the `minWithdrawable` field in the
lnurlw response. Some servers seem to set this to `null` instead of 0
when having no minimum withdrawal amount.
separates the resolving step from the QEInvoiceParser so the 'recipient'
can be resolved first and then either an QEInvoiceParser can be used if
it is a sending request that has been resolved (invoice, address,
lnurlp, ...), or RequestDetails can be used if the resolved 'recipient'
turns out to be a voucher/LNURLW string.
# Conflicts:
# electrum/gui/qml/qeinvoice.py
adds handling of lnurl-withdraw payment identifiers which allow users to
withdraw bitcoin from a service by scanning a qr code or pasting the
lnurl-w code as "sending" address.
- in lnurl.py, make request methods async
- in Qt GUI, lnurl network requests no longer block the GUI thread
- but they still do in the kivy GUI
- "lightning address" (LUD-16) support is removed for now as the
email addresses are indistinguishable from openalias email addresses
(both protocols should have added and enforced a prefix, or similar,
to remove this kind of ambiguity -- now we would need to make a
network request just to identify what kind of ID we were given)
f321x