gruel should allow for the changing of github labels on an action

[jwir3]

It would be nice if we had something like the following set up for a github environment:

github {
  auth_token="<YOUR SECRET KEY HERE>"
  repository="jwir3/gruel"
}

If we then had a general task, like GitHubTask, as well as more specific tasks that derived from GitHubTask, such as RemoveLabelTask, AddLabelTask, and ChangeAssigneeTask, we could do something like the following in our build.gradle:

  removeAssignee(type: ChangeAssigneeTask) {
    assignee = ''
  }

  removeDevelopingLabel(type: RemoveLabelTask) {
    labelName = 'developing'
  }

  addNeedsQALabel(type: AddLabelTask) {
    labelName = 'needs-qa'
  }

  uploadAlpha (dependsOn: [removeAssignee, removeDevelopingLabel, addNeedsQALabel])