add models for retraction

src/main/java/eu/siacs/conversations/xml/Namespace.java

@@ -91,6 +91,7 @@ public final class Namespace {
     public static final String REGISTER = "jabber:iq:register";
     public static final String REGISTER_STREAM_FEATURE = "http://jabber.org/features/iq-register";
     public static final String REPLY = "urn:xmpp:reply:0";
+    public static final String RETRACT = "urn:xmpp:message-retract:0";
     public static final String ROSTER = "jabber:iq:roster";
     public static final String SASL = "urn:ietf:params:xml:ns:xmpp-sasl";
     public static final String SASL_2 = "urn:xmpp:sasl:2";

src/main/java/im/conversations/android/database/model/PartType.java

@@ -2,5 +2,7 @@ package im.conversations.android.database.model;
 
 public enum PartType {
     TEXT,
-    FILE
+    FILE,
+    RETRACTION,
+    MODERATION
 }

src/main/java/im/conversations/android/xmpp/model/retract/Retract.java

@@ -0,0 +1,10 @@
+package im.conversations.android.xmpp.model.retract;
+
+import im.conversations.android.xmpp.model.Extension;
+
+public class Retract extends Extension {
+
+    public Retract() {
+        super(Retract.class);
+    }
+}

src/main/java/im/conversations/android/xmpp/model/retract/Retracted.java

@@ -0,0 +1,10 @@
+package im.conversations.android.xmpp.model.retract;
+
+import im.conversations.android.xmpp.model.Extension;
+
+public class Retracted extends Extension {
+
+    public Retracted() {
+        super(Retracted.class);
+    }
+}

src/main/java/im/conversations/android/xmpp/model/retract/package-info.java

@@ -0,0 +1,5 @@
+@XmlPackage(namespace = Namespace.RETRACT)
+package im.conversations.android.xmpp.model.retract;
+
+import eu.siacs.conversations.xml.Namespace;
+import im.conversations.android.annotation.XmlPackage;