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.

version.gradle

@@ -4,6 +4,6 @@ allprojects {
 		isSnapshot = true
 		jxmppVersion = '0.7.0-alpha5'
 		miniDnsVersion = '0.4.0-alpha3'
-		smackMinAndroidSdk = 9
+		smackMinAndroidSdk = 19
 	}
 }