Prevent adding multiple publications of same name to PublicationContainer
- More tests for maven-publish sad-day scenarios
Cross version test for web app published with maven-publish plugin
Added GroovyPublicationContainer that extends DefaultPublicationContainer and adds support for publication DSL
- Need to review if this is the right way to implement this, and if this should be made into a more generic feature
  on NamedDomainObjectContainer
Use instantiator to construct SoftwareComponentsContainer so it plays nicely in the DSL
Update docs and sample for new maven-publish DSL
Remove unused import