add lnurl-pay (LUD-06) support

[SomberNight]

This includes #7573 and #7683, and some clean-up commits.

Support for paying to "lnurl-pay" is added to the Qt and kivy GUIs.

"lightning address" (LUD-16) support is not added for now, mainly as the email-address-like format is ambiguous and cannot be distinguished from e.g. openalias.

Unlike in a previous version of this PR, in the Qt GUI, the network requests are not done on the GUI thread, instead they are async and use qt signals.
Re the kivy GUI, they are still running on the GUI thread and blocking the GUI. This can be fixed later or as a follow-up.

closes #7573
closes #7683

---

Re Qt paytoedit specifically, it seems hard to have good UX.
There are design questions, such as

• re user typing into the field, how do we know they are finished - e.g. when to validate the text or do network requests if needed
  • we could wait until the text field loses focus
  • we could start a timer on textChanged(), i.e. do network requests if user hasn't typed for e.g. 1 second
  • maybe add a dedicated button...
  • this PR takes the following approach:
    • add param to check_text to toggle if network requests are allowed ("full check")
    • every 0.5 sec, if the textedit has no focus, do full check
    • on textChanged()
      • detect if user copy-pasted by comparing current text against clipboard contents,
        if so, do full check
      • otherwise, do partial check
    • on clicking ButtonsWidget btns (scan qr, paste, read file), do full check
• note that "openalias" ids and "lightning address" ids can both look like email addresses and hence can collide. how to handle this?
  • we give priority to "lightning address" and do network request for that first
  • if that fails, we do "openalias" network request
  • "lightning address" support is postponed for now

---

Examples to test in Qt paytoedit:

• mempool@jhoenicke.de
  • this is both a valid "lightning address" and a valid "openalias"
  • https://jhoenicke.de/.well-known/lnurlp/mempool
• lnurl
  • lightning:lnurl1dp68gurn8ghj76ngdajku6trddjjuer99uh8wetvdskkkmn0wahz7mrww4excup0d4jk6ur0dakqhmhnx2
• bolt11
  • lnbc3680n1p3zka2ypp5nf74fk49ehwmqfdkwfn86q4pgytjttrdqa4gg64v7tntrf5ws9vsdpdg3hkuct5d9hkugrxdaezqjn0dphk2fmnypkk2mtsdahkccqzpgxqyz5vqsp5d69tlczphwcg62p9pc307yd59f2xacnkdhfsnxx3a7pgmhmmmg7q9qyyssqdnhpzxrhf47x5srjxmzv8wq7mkeuyca0lqy55vvfxxtqdguc67mhy9s8qhvn9fpmk65qs36e06gj3rmvslalf9mds8ptlssfnu5kkfspyrxu2p
• openalias
  • donate.getmonero.org
  • donate@getmonero.org
• bip70
  • bitcoin:?r=https://bitpay.com/i/5V4bqzj8xHs5UepqA9WCzw
• bitcoin address
  • bc1qq2tmmcngng78nllq2pvrkchcdukemtj56uyue0
• multi-line onchain outputs

  tb1qk3g0t9pw5wctkzz7gh6k3ljfuukn729s67y54e, 0.002
  tb1qr7evucrllljtryam6y2k3ntmlptq208pghql2h, 2!
  tb1qs3msqp0n0qade2haanjw2dkaa5lm77vwvce00h, 0.003
  tb1qar4ye43tdfj6y5n3yndp9adhs2wuz2v0wgqn5l, 3!