Added Javadoc publisher.
Merge remote-tracking branch 'eveoh/publisher-javadoc'

Conflicts:
	job-dsl-core/src/main/groovy/javaposse/jobdsl/dsl/helpers/publisher/PublisherContextHelper.groovy
	job-dsl-core/src/test/groovy/javaposse/jobdsl/dsl/helpers/publisher/PublisherHelperSpec.groovy