Add a simple test mode (#1181)

- [x] Provide data model and configuration toggle
- [x] Allow to delete individual test orders
- [x] Add tests
- [x] Add a prominent warning message to the backend if test mode orders exist (even though test mode is off), as this leads to wrong statistics
- [x] Decide if and how to generate invoices for test orders as invoice numbers cannot be repeated or should not have gaps.
- [x] Decide if and how we expose test orders through the API, since our difference pull mechanism relies on the fact that orders cannot be deleted.
- [x] Decide if and how we want to couple test modes of payment providers?
- [ ] pretix.eu: Ignore test orders for billing
- [ ] Adjust payment providers: Mollie, bitpay, cash, fakepayment, sepadebit

![download](https://user-images.githubusercontent.com/64280/53009081-fe420d80-343a-11e9-8361-b8511c988598.png)

src/pretix/presale/templates/pretixpresale/event/base.html

@@ -28,7 +28,7 @@
 {% endblock %}
 {% block page %}
     <div class="page-header">
-        {% if request.event.settings.organizer_link_back  %}
+        {% if request.event.settings.organizer_link_back %}
             <p>
                 <a href="{% eventurl request.organizer "presale:organizer.index" %}">
                     &laquo; {% blocktrans trimmed with name=request.organizer.name %}
@@ -64,6 +64,13 @@
         </div>
         <div class="clearfix"></div>
     </div>
+    {% if request.event.testmode %}
+        <div class="alert alert-warning">
+            <strong>
+                {% trans "This ticket shop is currently in test mode. Please do not perform any real purchases as your order might be deleted without notice." %}
+            </strong>
+        </div>
+    {% endif %}
     {% if messages %}
         {% for message in messages %}
             <div class="alert {{ message.tags }}">
@@ -73,6 +80,13 @@
     {% endif %}
     {% block content %}
     {% endblock %}
+    {% if request.event.testmode %}
+        <div class="alert alert-testmode alert-warning">
+            <strong>
+                {% trans "This ticket shop is currently in test mode. Please do not perform any real purchases as your order might be deleted without notice." %}
+            </strong>
+        </div>
+    {% endif %}
 {% endblock %}
 {% block footer %}
     {% if request.event.settings.contact_mail %}

src/pretix/presale/templates/pretixpresale/event/checkout_payment.html

@@ -31,6 +31,20 @@
                     <div id="payment_{{ p.provider.identifier }}"
                             class="panel-collapse collapsed {% if selected == p.provider.identifier %}in{% endif %}">
                         <div class="panel-body form-horizontal">
+                            {% if request.event.testmode %}
+                                {% if p.provider.test_mode_message %}
+                                    <div class="alert alert-info">
+                                        {{ p.provider.test_mode_message }}
+                                    </div>
+                                {% else %}
+                                    <div class="alert alert-warning">
+                                        {% trans "This payment provider does not provide support for testmode." %}
+                                        <strong>
+                                            {% trans "If you continue, actual money might be transferred." %}
+                                        </strong>
+                                    </div>
+                                {% endif %}
+                            {% endif %}
                             {{ p.form }}
                         </div>
                     </div>

src/pretix/presale/templates/pretixpresale/event/order.html

@@ -44,6 +44,9 @@
         {% blocktrans trimmed with code=order.code %}
             Your order: {{ code }}
         {% endblocktrans %}
+        {% if order.testmode %}
+            <span class="label label-warning">{% trans "TEST MODE" %}</span>
+        {% endif %}
         {% include "pretixpresale/event/fragment_order_status.html" with order=order class="pull-right" %}
         <div class="clearfix"></div>
     </h2>