Remove public trial fields from dossier and repository default views

As per [specification](https://my.teamraum.com/workspaces/onegov-gever-innovation-session/improvement-proposals/ogip6-umsetzung-offentlichkeitsgesetz/view) the fields `public_trial` and `public_trial_statement` must not be shown any more on the default views (*"Eigenschaften anzeigen"*) for dossiers and repository folders.

This pull request contains the necessary refactorings and changes to implement this requirement:

- Factor out browser ZCML into its own `configure.zcml` in `browser` package (dossier and repository)
- Override the `plone.dexterity` default view for all dexterity content (`IDexterityContent`) with a view and template that allow to define `omitted_fields` that are not shown.
- Default views for documents and dossiers have previously been customized (separately). Remove those views.
- Using this `omitted_fields` property, drop the public trial related fields from dossier and repository folder views
- Customize the default view for documents in order to restore the functionality that the widget for the `file` field is displayed in `NO_DOWNLOAD_DISPLAY_MODE`.
 
No, it's not necessary in my opinion. The responsible gets displayed slightly different than before, but better IMHO:
Before: `sk1m1`
After: `sk1m1 (Mandant 1 Sekretariat 1)`