Added query with comments and more model data.

- --comments flag is now available for queyring
- new mappings:
- - Account.username as String
- - Change.comments as List<Comment>
- - Comment.reviewer as Account
- - Comment.message as String
- - PatchSet.author as Account
- - PatchSet.approvals as List<Approval>
- - PatchSet.parents as List<String>
- replaced Approval.username (as String) by Approval.by (as Account)