add support for freezing utxos

src/main/java/com/sparrowwallet/drongo/wallet/BlockTransactionHashIndex.java

@@ -9,6 +9,7 @@ public class BlockTransactionHashIndex extends BlockTransactionHash implements C
     private final long index;
     private final long value;
     private BlockTransactionHashIndex spentBy;
+    private Status status;
 
     public BlockTransactionHashIndex(Sha256Hash hash, int height, Date date, Long fee, long index, long value) {
         this(hash, height, date, fee, index, value, null);
@@ -41,6 +42,14 @@ public class BlockTransactionHashIndex extends BlockTransactionHash implements C
         this.spentBy = spentBy;
     }
 
+    public Status getStatus() {
+        return status;
+    }
+
+    public void setStatus(Status status) {
+        this.status = status;
+    }
+
     @Override
     public String toString() {
         return getHash().toString() + ":" + index;

src/main/java/com/sparrowwallet/drongo/wallet/FrozenUtxoFilter.java

@@ -0,0 +1,8 @@
+package com.sparrowwallet.drongo.wallet;
+
+public class FrozenUtxoFilter implements UtxoFilter {
+    @Override
+    public boolean isEligible(BlockTransactionHashIndex candidate) {
+        return candidate.getStatus() == null || candidate.getStatus() != Status.FROZEN;
+    }
+}

src/main/java/com/sparrowwallet/drongo/wallet/Status.java

@@ -0,0 +1,5 @@
+package com.sparrowwallet.drongo.wallet;
+
+public enum Status {
+    FROZEN
+}