Added a System Groovy Script list choice provider.
Updated docs
Added error handling and return type checking
refs #21 Cherry picked @mrumpf 's pull request. Fixed indent letters.
refs #21 Japanize messages in SystemGroovyScript.
refs #21 changed copyright notices. SystemGroovyChoiceListProvider is a work of Michael Rumpf.
refs #21 Added Tests for SystemGroovyChoiceListProvider.
Merge branch 'feature/21_SystemGroovyScript'
Updated README.md.