Improve MUC Presence interceptors

Use PresenceListener as intercepting callback interface.

Remove the for-each loops in MultiUserChat by using the interception
facilities of the XMPPConnection.

Add ToFilter.

smack-core/src/main/java/org/jivesoftware/smack/filter/ToFilter.java

@@ -0,0 +1,41 @@
+/**
+ *
+ * Copyright © 2014 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smack.filter;
+
+import java.util.Locale;
+
+import org.jivesoftware.smack.packet.Packet;
+
+public class ToFilter implements PacketFilter {
+
+    private final String to;
+
+    public ToFilter(String to) {
+        this.to = to.toLowerCase(Locale.US);
+    }
+
+    @Override
+    public boolean accept(Packet packet) {
+        String packetTo = packet.getTo();
+        if (packetTo == null) {
+            return false;
+        }
+        packetTo = packetTo.toLowerCase(Locale.US);
+        return packetTo.equals(to);
+    }
+
+}