Simplified Roster

Removed some throw declarations from methods, so some try/catch blocks
could be removed.

Use switch/case instead of if/else if.

Make members final when possible.

Add logger statements in case of error IQ result and remove superfluous
check of instanceof IQ.

smack-tcp/src/test/java/org/jivesoftware/smack/RosterOfflineTest.java

@@ -46,11 +46,6 @@ public class RosterOfflineTest {
         roster.createEntry("test", "test", null);
     }
 
-    @Test(expected = SmackException.class)
-    public void shouldThrowExceptionOnCreateGroup() throws Exception {
-        roster.createGroup("test");
-    }
-
     @Test(expected = SmackException.class)
     public void shouldThrowExceptionOnReload() throws Exception {
         roster.reload();