Add remote delete info to json output

Fixes #424

src/main/java/org/asamk/signal/json/JsonRemoteDelete.java

@@ -0,0 +1,15 @@
+package org.asamk.signal.json;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import org.whispersystems.signalservice.api.messages.SignalServiceDataMessage;
+
+class JsonRemoteDelete {
+
+    @JsonProperty
+    final long timestamp;
+
+    JsonRemoteDelete(SignalServiceDataMessage.RemoteDelete remoteDelete) {
+        this.timestamp = remoteDelete.getTargetSentTimestamp();
+    }
+}