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)
