[#3005] Add group follow, unfollow and followers pages

These are not properly integrated into the frontend yet: no
follow/unfollow buttons on the group pages, no link to group followers
page, group followers page does not look right. But they work.

ckan/config/routing.py

@@ -237,7 +237,10 @@ def make_map():
           'edit',
           'authz',
           'delete',
-          'history'
+          'history',
+          'followers',
+          'follow',
+          'unfollow',
           ]))
           )
         m.connect('group_read', '/group/{id}', action='read')

ckan/controllers/group.py

@@ -498,6 +498,56 @@ def history(self, id):
             return feed.writeString('utf-8')
         return render(self._history_template(c.group_dict['type']))
 
+    def follow(self, id):
+        '''Start following this group.'''
+        context = {'model': model,
+                   'session': model.Session,
+                   'user': c.user or c.author}
+        data_dict = {'id': id}
+        try:
+            get_action('follow_group')(context, data_dict)
+            h.flash_success(_("You are now following {0}").format(id))
+        except ValidationError as e:
+            error_message = (e.extra_msg or e.message or e.error_summary
+                    or e.error_dict)
+            h.flash_error(error_message)
+        except NotAuthorized as e:
+            h.flash_error(e.extra_msg)
+        h.redirect_to(controller='group', action='read', id=id)
+
+    def unfollow(self, id):
+        '''Stop following this group.'''
+        context = {'model': model,
+                   'session': model.Session,
+                   'user': c.user or c.author}
+        data_dict = {'id': id}
+        try:
+            get_action('unfollow_group')(context, data_dict)
+            h.flash_success(_("You are no longer following {0}").format(id))
+        except ValidationError as e:
+            error_message = (e.extra_msg or e.message or e.error_summary
+                    or e.error_dict)
+            h.flash_error(error_message)
+        except (NotFound, NotAuthorized) as e:
+            error_message = e.extra_msg or e.message
+            h.flash_error(error_message)
+        h.redirect_to(controller='group', action='read', id=id)
+
+    def followers(self, id=None):
+        context = {'model': model, 'session': model.Session,
+                   'user': c.user or c.author, 'for_view': True}
+        data_dict = {'id': id}
+        try:
+            c.group_dict = get_action('group_show')(context, data_dict)
+            c.followers = get_action('group_follower_list')(context,
+                    {'id': c.group_dict['id']})
+        except NotFound:
+            abort(404, _('Group not found'))
+        except NotAuthorized:
+            abort(401, _('Unauthorized to read group %s') % id)
+
+        return render('group/followers.html')
+
     def _render_edit_form(self, fs):
         # errors arrive in c.error and fs.errors
         c.fieldset = fs

ckan/templates/group/followers.html

@@ -0,0 +1,10 @@
+{% extends "page.html" %}
+
+{% block subtitle %}{{ _('Followers') }} - {{ c.group_dict.title or c.group_dict.name }}{% endblock %}
+
+{% block primary_content %}
+  <section class="module-content">
+    <h1 class="hide-heading">{{ _('Followers') }}</h1>
+    {% snippet "user/snippets/followers.html", followers=c.followers %}
+  </section>
+{% endblock %}