WebComment: update & fix get_first_... function

* Updates and fixes template functions in WebComment so that
  `get_first_comments_or_remarks` is not broken anymore. (closes #2522)
Merge branch 'master-2522-fix-get_first_comments_or_remarks' of https://github.com/kasioumis/invenio into prod

Conflicts:
	modules/webcomment/lib/webcomment_templates.py