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.

build.gradle

@@ -102,7 +102,7 @@ allprojects {
 		junitVersion = '5.2.0'
 	}
 	group = 'org.igniterealtime.smack'
-	sourceCompatibility = 1.7
+	sourceCompatibility = JavaVersion.VERSION_1_8
 	targetCompatibility = sourceCompatibility
 	version = shortVersion
 	if (isSnapshot) {
@@ -245,7 +245,14 @@ gradle.taskGraph.whenReady { taskGraph ->
 	}
 }
 
-task javadocAll(type: Javadoc) {
+task copyAllJavadocDocFiles(type: Copy) {
+	from javadocAllProjects.collect { project ->
+		"${project.projectDir}/src/javadoc" }
+	into javadocAllDir
+	include '**/doc-files/*.*'
+}
+
+task javadocAll(type: Javadoc, dependsOn: copyAllJavadocDocFiles) {
 	source javadocAllProjects.collect {project ->
 		project.sourceSets.main.allJava }
 	destinationDir = javadocAllDir
@@ -449,12 +456,39 @@ subprojects {
 		enabled false
 		semver false
 	}
+
+	// Work around https://github.com/gradle/gradle/issues/4046
+	javadoc.dependsOn('copyJavadocDocFiles')
+	task copyJavadocDocFiles(type: Copy) {
+		from('src/javadoc')
+		into 'build/docs/javadoc'
+		include '**/doc-files/*.*'
+	}
+
+	// If this subproject has a Makefile then make copyJavadocDocFiles
+	// and the root project's javadocAll task dependend on
+	// generateFiles.
+	if (file("$projectDir/Makefile").exists()) {
+		copyJavadocDocFiles.dependsOn('generateFiles')
+		rootProject.copyAllJavadocDocFiles.dependsOn("${project.name}:generateFiles")
+		task generateFiles(type: Exec) {
+			workingDir projectDir
+			commandLine 'make'
+		}
+
+		clean.dependsOn('cleanGeneratedFiles')
+		rootProject.clean.dependsOn("${project.name}:cleanGeneratedFiles")
+		task cleanGeneratedFiles(type: Exec) {
+			workingDir projectDir
+			commandLine 'make', 'clean'
+		}
+	}
 }
 
 configure (androidProjects + androidBootClasspathProjects) {
 	apply plugin: 'ru.vyarus.animalsniffer'
 	dependencies {
-		signature "net.sf.androidscents.signature:android-api-level-${smackMinAndroidSdk}:2.3.1_r2@signature"
+		signature "net.sf.androidscents.signature:android-api-level-${smackMinAndroidSdk}:4.4.2_r4@signature"
 	}
 	animalsniffer {
 		sourceSets = [sourceSets.main]