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-integration-test/src/main/java/org/jivesoftware/smackx/ox/AbstractOpenPgpIntegrationTest.java

@@ -41,7 +41,7 @@ public abstract class AbstractOpenPgpIntegrationTest extends AbstractSmackIntegr
     protected final PepManager bobPepManager;
     protected final PepManager chloePepManager;
 
-    protected AbstractOpenPgpIntegrationTest(SmackIntegrationTestEnvironment environment)
+    protected AbstractOpenPgpIntegrationTest(SmackIntegrationTestEnvironment<?> environment)
             throws XMPPException.XMPPErrorException, TestNotPossibleException, SmackException.NotConnectedException,
             InterruptedException, SmackException.NoResponseException {
         super(environment);

smack-integration-test/src/main/java/org/jivesoftware/smackx/ox/OXSecretKeyBackupIntegrationTest.java

@@ -97,7 +97,7 @@ public class OXSecretKeyBackupIntegrationTest extends AbstractOpenPgpIntegration
      * @throws InterruptedException
      * @throws SmackException.NoResponseException
      */
-    public OXSecretKeyBackupIntegrationTest(SmackIntegrationTestEnvironment environment)
+    public OXSecretKeyBackupIntegrationTest(SmackIntegrationTestEnvironment<?> environment)
             throws XMPPException.XMPPErrorException, TestNotPossibleException, SmackException.NotConnectedException,
             InterruptedException, SmackException.NoResponseException {
         super(environment);