Comments extensions to keep comments on CKAN server

Currently the only working comments extension is [ckanext-disqus](https://github.com/ckan/ckanext-disqus), which uses an external commenting provider and system for data storing. For various reasons [1] a comments extension would be very nice, that **stores the comments in the CKAN backend itself**.

There is an approach for such an extension with [ckanext-comments](https://github.com/rossjones/ckanext-comments). Maybe [Isso](http://posativ.org/isso/) could also be used.

[1] See also this [discussion on mailinglist](https://lists.okfn.org/pipermail/ckan-dev/2014-April/007288.html).

Start by reviewing the linked ckanext-comments approach and the Isso project, then read the linked mailing-list discussion for requirements and constraints. The issue does not name files, tests, or a CKAN entry point; completion would require defining and implementing a supported comments extension that stores comments in the CKAN backend.

Written by the indexing model from the issue text.