anchors: switch to zero-fee-htlcs

* sets the weight of htlc transactions to zero, thereby putting a zero
  fee for the htlc transactions
* add inputs to htlc-tx for fee bumping
* switches feature flags
* disable anchor test vectors, which are now partially invalid

electrum/util.py

@@ -145,6 +145,11 @@ class NotEnoughFunds(Exception):
         return _("Insufficient funds")
 
 
+class UneconomicFee(Exception):
+    def __str__(self):
+        return _("The fee for the transaction is higher than the funds gained from it.")
+
+
 class NoDynamicFeeEstimates(Exception):
     def __str__(self):
         return _('Dynamic fee estimates not available')