Moved JavadocArtifact from language-jvm -> language-java
Moved Groovydoc, AntGroovydoc and GroovydocTest back to ‘plugins’ for now

- Don't want to move into 'language-groovy' until the tasks have been converted to java
Renamed platform-base/src/main/groovy => src/main/java
Moved language-jvm/src/main/groovy -> src/main/java