Merge pull request #222 from fredericbonjour/Admin

Changed template format for <preview/> in <rbs-document-list/>.
Cleaned document picker templates.
Enhanced FormsManager:
- added cascadeEditor() method to ease the cascading of a document (existing or new)
- added cascadeEdit(doc) and cascadeCreate(modelName or doc) in Editors' scope (directly available in the template).

Enhanced Editors: added possibility to hide a section in the MainMenu when a document is being created (add 'hide-when-create="true"' on the <fieldset/> in the Editor template).