Create smack-im subproject for XMPP-IM

Move Roster and Chat(Manager) code into their own packages within the
new smack-im subproject.

Apply Manager pattern to Roster.

Fixes SMACK-637.

smack-im/src/main/java/org/jivesoftware/smack/im/SmackImInitializer.java

@@ -0,0 +1,33 @@
+/**
+ *
+ * Copyright © 2015 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.im;
+
+import org.jivesoftware.smack.initializer.UrlInitializer;
+
+public class SmackImInitializer extends UrlInitializer {
+
+    @Override
+    protected String getProvidersUrl() {
+        return "classpath:org.jivesoftware.smack.im/smackim.providers";
+    }
+
+    @Override
+    protected String getConfigUrl() {
+        return "classpath:org.jivesoftware.smack.im/smackim.xml";
+    }
+
+}