Add fieldsets of placeholders to the list of already
        existing fieldsets.

def get_fieldsets(self, request, obj=None):
        """
        Add fieldsets of placeholders to the list of already
        existing fieldsets.
        """

        # some ugly business to remove freeze_date
        # from the field list
        general_module = {
            'fields': list(self.general_fields),
            'classes': ('module-general',),
        }

        default_fieldsets = list(self.fieldsets)
        if not request.user.has_perm('pages.can_freeze'):
            general_module['fields'].remove('freeze_date')
        if not request.user.has_perm('pages.can_publish'):
            general_module['fields'].remove('status')

        default_fieldsets[0][1] = general_module

        placeholder_fieldsets = []
        template = get_template_from_request(request, obj)
        for placeholder in get_placeholders(template):
            if placeholder.name not in self.mandatory_placeholders:
                placeholder_fieldsets.append(placeholder.name)

        additional_fieldsets = []

        # meta fields
        metadata_fieldsets = [f['name'] for f in self.metadata_fields]
        additional_fieldsets.append((_('Metadata'), {
            'fields': metadata_fieldsets,
            'classes': ('module-content', 'grp-collapse grp-closed'),
        }))
        additional_fieldsets.append((_('Content'), {
            'fields': placeholder_fieldsets,
            'classes': ('module-content',),
        }))

        return default_fieldsets + additional_fieldsets