Better editing support for groovy files that are not on the build path

Currently, we explicitly disable much of the editing support for Groovy files that are not on the build path. This means that editing scripts, gradle files, or anything else not on the build path will not be too easy. Since we are trying to provide better gradle support, we should be doing something about this.

It would be nice to enable standard editor features like navigation, outline view, content assist, type inferencing, and dsl support.

I don't remember exactly why we disabled this in the past, but I do know that there were many exceptions being added to the log when editing files not on the build path.