Dokumenten-Tab mit Öffentlichkeitsstatus erweitern

Anpassungen an TabbedView Konfiguration
 - [ ] "public trial"-Spalte in Dokumenten-Tab hinzufügen
https://github.com/4teamwork/opengever.core/blob/master/opengever/tabbedview/browser/tabs.py#L177
 - [ ] Werte übersetzt darstellen: https://github.com/4teamwork/opengever.core/blob/master/opengever/task/helper.py

Index und Metadaten hinzufügen:
http://docs.plone.org/develop/plone/searching_and_indexing/indexing.html
 - [ ] Neuer Katalog-Index `public_trial` index in [indexes.py](https://github.com/4teamwork/opengever.core/blob/master/opengever/document/indexers.py#L107) 
 - [ ] Katalog Metadata `public_trial` metadata in [catalog.xml](https://github.com/4teamwork/opengever.core/blob/master/opengever/document/profiles/default/catalog.xml) eintragen (muss reindexiert werden) 
 - [ ] Custom Sorter [opengever.tabbedview.tabs](https://github.com/4teamwork/opengever.core/blob/master/opengever/tabbedview/browser/tabs.py#L132)
  * Upgrade-Step
    - [ ] `public_trial` index [neu rechnen] (https://github.com/4teamwork/ftw.upgrade#upgrade-step-helpers) `catalog_reindex_objects` (mit logger)
    - [ ] `public_trial` metadata per profil (catalog.xml) hinzufügen.