Add estimated tx fee to amount check when posting bid.

Add more log messages around balance checks.

basicswap/interface/btc.py

@@ -217,6 +217,10 @@ class BTCInterface(Secp256k1Interface):
             rv += output.nValue
         return rv
 
+    @staticmethod
+    def est_lock_tx_vsize() -> int:
+        return 110
+
     @staticmethod
     def xmr_swap_a_lock_spend_tx_vsize() -> int:
         return 147