core&ui: add group bulk import/export

packages/ui-default/templates/domain_group.html

@@ -4,6 +4,8 @@
   <div class="section__header">
     <h1 class="section__title">{{ _('{0}: Groups').format(domain.name) }}</h1>
     <div class="section__tools">
+      <button class="rounded button" name="import_groups">{{ _('Import Groups') }}</button>
+      <button class="rounded button" name="export_groups">{{ _('Export Groups') }}</button>
       <button class="primary rounded button" name="create_group">{{ _('Create Group') }}</button>
     </div>
   </div>