ToDo
====

  [X] Create basic dexterity-based collection type.

  [X] Use QueryStringWidget (plone.formwidget.querystring) for the query field.

  [X] Make sure the edit view is fully functional.

  [X] Re-create class/view methods of the old collection type.

  [X] Make the standard collection views work.

  [X] Make enableSyndication/RSS work. Syndication is not working for
      plone.app.collection trunk either.

  [ ] Refactor plone.formwidget.querystring to not use sorting field
      duplicates as described here: https://github.com/plone/plone.formwidget.querystring/blob/master/plone/formwidget/querystring/querywidget.js#L222
      The '@@querybuilder_html_results' view from plone.app.querystring should
      use the z3c.form fields directly.

  [ ] Make the tabular_view and the in-out-widget for the customViewFields field work.

  [ ] Make the collection portlet work.