Change template extension build mechanism to Gradle
Converts extension to Gradle build mechanism
Merge branch 'master' into develop

Conflicts:
	.classpath
	.gitignore
	.project
	build.gradle
	gradle.properties
	src/main/java/com/rapidminer/PluginInitTemplate.java
Fixes errors introduced by merging develop into master
Adds jcenter as default Maven repository to build.gradle
Adds public RapidMiner Bintray repository
Change RapidMiner dependency to version 5.3.0, use public and open-source Maven RapidMiner Bintray repository, adds VLdocking dependency