Added convenience constants to JavaSourceSet.
JavaSourceGroupName now has an OTHER type rather than an ALL type.
Upgraded the Tooling API to the latest nightly in "netbeans-gradle-default-models" and added another very basic test.
Refactored the plugin to allow supporting the new API. There are lots of TODOs currently, which need to be addressed not to cause regression.
Some cleanup after refactoring.
JavaSourcesModelBuilder now has two possible instances (to allow retrieving models without runtime dependencies).