SmackReactor/NIO, Java8/Android19, Pretty print XML, FSM connections

This commit adds
- SmackReactor / NIO
- a framework for finite state machine connections
- support for Java 8
- pretty printed XML debug output

It also
- reworks the integration test framework
- raises the minimum Android API level to 19
- introduces XmppNioTcpConnection

Furthermore fixes SMACK-801 (at least partly). Java 8 language
features are available, but not all runtime library methods. For that
we would need to raise the Android API level to 24 or higher.

smack-bosh/src/main/java/org/jivesoftware/smack/bosh/XMPPBOSHConnection.java

@@ -387,18 +387,6 @@ public class XMPPBOSHConnection extends AbstractXMPPConnection {
         readerConsumer.start();
     }
 
-    /**
-     * Sends out a notification that there was an error with the connection
-     * and closes the connection.
-     *
-     * @param e the exception that causes the connection close event.
-     */
-    protected void notifyConnectionError(Exception e) {
-        // Closes the connection temporary. A reconnection is possible
-        shutdown();
-        callConnectionClosedOnErrorListener(e);
-    }
-
     /**
      * A listener class which listen for a successfully established connection
      * and connection errors and notifies the BOSHConnection.