Add support for the `golang` plugin

Add support for the [Golang Plugin](https://wiki.jenkins-ci.org/display/JENKINS/Go+Plugin).
cleanup
Merge branch 'golang'

Conflicts:
	docs/Home.md
	docs/Job-reference.md
	job-dsl-core/src/main/groovy/javaposse/jobdsl/dsl/helpers/wrapper/WrapperContext.groovy
	job-dsl-core/src/test/groovy/javaposse/jobdsl/dsl/helpers/wrapper/WrapperContextSpec.groovy