LN invoice: better handle unknown required featured bits in bolt11 invs

A user provided an invoice that requires feature bit 30. (That bit is not in the spec)
To test:
```
lnbc1p324a66pp5tundykxx3q5kztsr8x00eknpn2uwe3394cnky3j9a0fswm568wnsdp9facx2mj5d9kk2um5v9khqueqv3hkuct5d9hkucqzpgxq9z0rgqsp5l73jgfgctzc92juer5rk2mqcrkj8teng53dr9vfxj4n8lulu4jmq9q8pqqqssq4gacn859tpzz99hkusnh7m93d5ncpx3t4zns8ynca7akmljpl5vh504qjz7dqwewqjh4md7xagaz5wg85knvxywrhp0sp2t09yta7lcq3qs6fy

lntb1p324a66pp5tundykxx3q5kztsr8x00eknpn2uwe3394cnky3j9a0fswm568wnssp5l73jgfgctzc92juer5rk2mqcrkj8teng53dr9vfxj4n8lulu4jmqdp9facx2mj5d9kk2um5v9khqueqv3hkuct5d9hkuxq9z0rgq9q8pqqqssqdte0z9dy7ur7fagsk7r3mtfj6upq88xfylhufys87zqpamklcfgn2f3xeq3nlhvn3qy9tdgg42vq9eq99qz6rz6tzqezfhzuv6zsr5qp7cgel4
```

electrum/gui/kivy/uix/screens.py

@@ -16,6 +16,7 @@ from electrum.invoices import (PR_DEFAULT_EXPIRATION_WHEN_CREATING,
                                PR_PAID, PR_UNKNOWN, PR_EXPIRED, PR_INFLIGHT,
                                pr_expiration_values, Invoice)
 from electrum import bitcoin, constants
+from electrum import lnutil
 from electrum.transaction import tx_from_any, PartialTxOutput
 from electrum.util import (parse_URI, InvalidBitcoinURI, TxMinedInfo, maybe_extract_lightning_payment_identifier,
                            InvoiceError, format_time, parse_max_spend, BITCOIN_BIP21_URI_SCHEME)
@@ -224,6 +225,9 @@ class SendScreen(CScreen, Logger):
         except LnInvoiceException as e:
             self.app.show_info(_("Invoice is not a valid Lightning invoice: ") + repr(e)) # repr because str(Exception()) == ''
             return
+        except lnutil.IncompatibleOrInsaneFeatures as e:
+            self.app.show_info(_("Invoice requires unknown or incompatible Lightning feature") + f":\n{e!r}")
+            return
         self.address = invoice
         self.message = lnaddr.get_description()
         self.amount = self.app.format_amount_and_units(lnaddr.amount * bitcoin.COIN) if lnaddr.amount else ''