Add a layout widget type supporting mode switch

add a configurable boolean property that makes it possible to switch the layout mode between edit and view modes + handle enclosing form

Needed properties:

• initialLayoutName + toggledLayoutName (toggled layout name defaults initial layout name if not filled)
• styleClass (div around the layout)
• toggle mode button label (defaults to 'Edit', translated when widget is translated)
• cancel toggle mode button label (defaults to 'Cancel', translated when widget is translated)
• hideDefaultActions: boolean to hide the default edit button
• additional actions category: to add custom actions on the toggled layout view
• buttons display, as in custom actions widget type (If set to 'buttons', actions will be displayed as command buttons. If set to 'links', actions will be displayed as command links. If set to 'icons', actions will be displayed as icons. Else (default behaviour), actions will be displayed as command links and display their icons when defined.)
• useAjaxForm (defaults to false)
• toggleEnabled: EL expression resolving to a boolean, defaults to "check permission WRITE on document"
  + boolean control on versioning and comment fields (see if this would be better to add them as widgets in the layout itself, note that commet field retrieval for audit logs may not be handled by automation chains => to check)

additional properties that should not be exposed right now:

• foldable (handled by the layout template directly)
• foldable bar class (same)
• initial mode (defaults to view) => do not expose in Studio right now
• toggled mode (defaults to edit) => same