Fix JENKINS-16916

- Updated ScriptContent to use better groovy setup.
- In default groovy script, add all content types as closures, these can
  be used like ${ENV(var: "BUILD_ID")} in the groovy template
Merge branch 'master' of https://github.com/jenkinsci/email-ext-plugin

Conflicts:
	src/main/resources/hudson/plugins/emailext/ExtendedEmailPublisher/config.groovy