Label ID missing from API, needed for Notes

Summary

The Label API does not expose the label id, which is desired/required for client functionality. In particular, the label ID is exposed via the Notes API in terms of body: "Added ~666 label". Please expose label ID in the Label API to allow lookup.

Steps to reproduce

1. GET /projects/:id/issues/:issue_id/notes
2. GET /projects/:id/labels

Expected behavior

Response from step (2) includes label id.

[
   {
      "id": 666, # <<<<<<<< need this
      "name" : "bug",
      "color" : "#d9534f",
      "description": "Bug reported by user",
      "open_issues_count": 1,
      "closed_issues_count": 0,
      "open_merge_requests_count": 1
   }
]

Actual behavior

No ID.

Results of GitLab environment info

Using GitLab.com.

Possible fixes

Is it sufficient to just add :id to here: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/api/entities.rb#L438