Allow specifying task group like project.task(name: "name", group: "group")

I believe it would be nice to be able to specify task group in creation options map, much like the name, description, type, dependencies etc. Like this:

project.task(name: "name", description: "description", group: "group", type: Type)

It is a small change which I was able to do myself, it's in my GitHub fork of Gradle: https://github.com/Ladicek/gradle/tree/task-group-in-creation-options-map. Test included. I will issue a pull request right after I create this JIRA issue.