Refs #39 -- New concept of "teams" (#478)

* New models

* CRUD UI

* UI for adding/removing team members

* Log display for teams

* Fix invitations, move frontend

* Drop old models (incomplete)

* Drop more old stuff

* Drop even more old stuff

* Fix tests

* Fix permission test

* flake8 fix

* Add tests fore the new code

* Rebase migrations

src/pretix/control/templates/pretixcontrol/event/base.html

@@ -10,7 +10,7 @@
             {% trans "Dashboard" %}
         </a>
     </li>
-    {% if request.eventperm.can_change_settings or request.eventperm.can_change_permissions %}
+    {% if 'can_change_event_settings' in request.eventpermset or 'can_change_permissions' in request.eventpermset %}
         <li>
             <a href="{% url 'control:event.settings' organizer=request.event.organizer.slug event=request.event.slug %}">
                 <i class="fa fa-wrench fa-fw"></i>
@@ -18,7 +18,7 @@
             </a>
         </li>
     {% endif %}
-    {% if request.eventperm.can_change_items %}
+    {% if 'can_change_items' in request.eventpermset %}
         <li>
             <a href="{% url 'control:event.items' organizer=request.event.organizer.slug event=request.event.slug %}"
                 class="has-children">
@@ -55,7 +55,7 @@
             </ul>
         </li>
     {% endif %}
-    {% if request.eventperm.can_view_orders %}
+    {% if 'can_view_orders' in request.eventpermset %}
         <li>
             <a href="{% url 'control:event.orders' organizer=request.event.organizer.slug event=request.event.slug %}"
                 class="has-children">
@@ -93,7 +93,7 @@
             </ul>
         </li>
     {% endif %}
-    {% if request.eventperm.can_view_vouchers %}
+    {% if 'can_view_vouchers' in request.eventpermset %}
         <li>
             <a href="{% url 'control:event.vouchers' organizer=request.event.organizer.slug event=request.event.slug %}"
                     {% if url_name == "event.vouchers" %}class="active"{% endif %}>