New REST api endpoints for reading published comments

Similar to existing drafts endpoints, but for published comments.
Published comments only support GET requests.  The payload is shared
between drafts and comments, with the latter including the author.

Add associated unit test.  Update REST api docs.

Bug: Issue 1820
Change-Id: Ie88cb334005d3d31ff48092bc40b6eab005eb687
13 files changed