Provide a (semi-)automated way to add ant-XXX.jar to the classpath

The AntBuilder class provides an easy way to generate ant scripts. This class is available out of the box on the command line since the ant jar is included on the classpath. However, we do not include ant inside of Groovy-Eclipse. And this makes it slightly more difficult for users to use the AntBuilder from within Eclipse because they need to manually add the jar to the project.

I propose that we include the ant jar with Groovy-Eclipse and provide an option to add the jar to the project's classpath from the new project wizard. The jar should be included in the Groovy classpath container. There should also be a way from within the container to configure whether or not the container should include the jar.