[IMP] website_event: Label 'Participating' on frontend

On the event page and on the event list page on a website, add a
label "participating" for the logged users that are participating
to the event to avoid mistakenly double-subscribing. But we don't
hard-prevent it, because it should still be possible to subscribe someone else.

Small improvement: The portal group in general settings was hidden. We set it
visible because it contains some useful options like 'Allow external users to
sign up'

addons/base_setup/res_config_view.xml

@@ -25,7 +25,7 @@
                             </div>
                         </div>
                     </group>
-                    <group groups="base.group_no_one">
+                    <group>
                         <label for="id" string="Portal access"/>
                         <div>
                             <div>

addons/website_event/models/event.py

@@ -22,6 +22,15 @@ class event(models.Model):
         string='Website Messages',
         help="Website communication history",
     )
+    is_participating = fields.Boolean("Is Participating", compute="_compute_is_participating")
+
+    def _compute_is_participating(self):
+        # we don't allow public user to see participating label
+        if self.env.user != self.env.ref('base.public_user'):
+            email = self.env.user.partner_id.email
+            for event in self:
+                domain = ['&', '|', ('email', '=', email), ('partner_id.email', '=', email), ('event_id', '=', event.id)]
+                event.is_participating = self.env['event.registration'].search_count(domain)
 
     @api.multi
     @api.depends('name')

addons/website_event/views/website_event.xml

@@ -58,6 +58,7 @@
                             <div itemscope="itemscope" itemtype="http://schema.org/Event" class="media-body">
                                 <h4 class="media-heading">
                                     <a itemprop="url" t-att-class="event.state == 'done' and 'text-success'" t-attf-href="/event/#{ slug(event) }/#{(not event.menu_id) and 'register' or ''}"><span itemprop="name" t-field="event.name"> </span></a>
+                                    <small t-if="event.is_participating" class="label label-info">Participating</small>
                                     <small t-if="not event.address_id" class="label label-info">Online</small>
                                     <small t-if="not event.website_published" class="label label-danger">not published</small>
                                 </h4>
@@ -268,6 +269,9 @@
     <t t-call="website_event.layout">
         <div itemscope="itemscope" itemtype="http://schema.org/Event" class="container">
             <h1 itemprop="name" class="text-center" t-field="event.name"></h1>
+            <div class="text-center">
+                <small t-if="event.is_participating" class="label label-info">Participating</small>
+            </div>
             <h4 class="text-center text-muted">
                 <i class="fa fa-clock-o"></i>
                 <span itemprop="startDate"><t t-esc="event.date_begin_located[:-3]"/></span> to