A new config API is introduced, and ~all of the codebase is adapted to it.
The old API is kept but mainly only for dynamic usage where its extra flexibility is needed.
Using examples, the old config API looked this:
```
>>> config.get("request_expiry", 86400)
604800
>>> config.set_key("request_expiry", 86400)
>>>
```
The new config API instead:
```
>>> config.WALLET_PAYREQ_EXPIRY_SECONDS
604800
>>> config.WALLET_PAYREQ_EXPIRY_SECONDS = 86400
>>>
```
The old API operated on arbitrary string keys, the new one uses
a static ~enum-like list of variables.
With the new API:
- there is a single centralised list of config variables, as opposed to
these being scattered all over
- no more duplication of default values (in the getters)
- there is now some (minimal for now) type-validation/conversion for
the config values
closes https://github.com/spesmilo/electrum/pull/5640
closes https://github.com/spesmilo/electrum/pull/5649
Note: there is yet a third API added here, for certain niche/abstract use-cases,
where we need a reference to the config variable itself.
It should only be used when needed:
```
>>> var = config.cv.WALLET_PAYREQ_EXPIRY_SECONDS
>>> var
<ConfigVarWithConfig key='request_expiry'>
>>> var.get()
604800
>>> var.set(3600)
>>> var.get_default_value()
86400
>>> var.is_set()
True
>>> var.is_modifiable()
True
```
The app hangs indefinitely if we try to quit it while one of
these threads is active, because once asyncio has shut down,
futures never return. This was already fixed for lightning
payments in c5dc133, but there are many other cases.
QEInvoice/QEInvoiceParser now properly split for mapping to Invoice type (QEInvoice)
and parsing/resolving of payment identifiers (QEInvoiceParser).
additionally, old, unused QEUserEnteredPayment was removed.
invoices are now never saved with user-entered amount if the original invoice
did not specify an amount (e.g. address-only, no-amount bip21 uri, or no-amount
lightning invoice). Furthermore, QEInvoice now adds an isSaved property so the
UI doesn't need to infer that from the existence of the invoice key.
Payments of lightning invoices are now triggered through QEInvoice.pay_lightning_invoice(),
using the internally kept Invoice instance. This replaces the old call path of
QEWallet.pay_lightning_invoice(invoice_key) which required the invoice to be saved
in the backend wallet before payment.
The LNURLpay flow arriving on InvoiceDialog implicitly triggered payment, this is
now indicated by InvoiceDialog.payImmediately property instead of inferrred from the
QEInvoiceParser isLnurlPay property.
'last' property on WizardComponents is now queried from UI, not from the wizard.
This allows the content of the WizardComponent itself to be taken into account.
