Allow public trial state to also be modified in closed dossier states

To achieve this, we implement a special edit form, which only handles the public trial field.
The link is only visible on the overview tab, if the dossier is in a closed state and the user has "modify portal content" permission in a open dossier state. 

- [x] Implement special edit form (for document and mail)
- [x] Implement edit button on overview tab (document / mail)
- [x] Translations
- [x] One of the parents of a document, needs to be a dossier
- [x] Hide public_trial on Repository and Dossier.
- [x] Merge https://github.com/4teamwork/plonetheme.teamraum/pull/224 (edit actions styling)
- [x] Refactor finding parent dossier (Move from opengever.mail into opengever.base.utils)

Further changes:
- The method find_parent_dossier now raises a ValueError if no dossier can be found.
- Small fix: https://github.com/4teamwork/opengever.core/pull/380/files#diff-7da5cf208796cf0c091e317a4e37ad85L37