add VoidWallet and make it the default.

lnbits/wallets/void.py

@@ -0,0 +1,19 @@
+from typing import Optional
+
+from .base import InvoiceResponse, PaymentResponse, PaymentStatus, Wallet, Unsupported
+
+
+class VoidWallet(Wallet):
+    def create_invoice(
+        self, amount: int, memo: Optional[str] = None, description_hash: Optional[bytes] = None
+    ) -> InvoiceResponse:
+        raise Unsupported("")
+
+    def pay_invoice(self, bolt11: str) -> PaymentResponse:
+        raise Unsupported("")
+
+    def get_invoice_status(self, checking_id: str) -> PaymentStatus:
+        raise Unsupported("")
+
+    def get_payment_status(self, checking_id: str) -> PaymentStatus:
+        raise Unsupported("")