Fixed typos and a little phrasing. (#175)

Mostly in German translation, some small fixes in English text, too.

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

@@ -61,8 +61,7 @@
                 {% if can_download %}
                     <p>
                         {% blocktrans trimmed %}
-                            Please use the buttons below to obtain your ticket. Please have your ticket ready when
-                            entering the event.
+                            Please obtain your ticket below. Please have your ticket ready when entering the event.
                         {% endblocktrans %}
                     </p>
                     {% for b in download_buttons %}

src/pretix/presale/templates/pretixpresale/organizers/index.html

@@ -58,4 +58,4 @@
         </table>
     </div>
     {% include "pretixpresale/pagination.html" %}
-{% endblock %}
+{% endblock %}

src/pretix/presale/views/async.py

@@ -128,7 +128,7 @@ class AsyncAction:
 
     def get_error_message(self, exception):
         logger.error('Unexpected exception: %r' % exception)
-        return _('An unexpected error has occured')
+        return _('An unexpected error has occured.')
 
     def get_success_message(self, value):
-        return _('The task has been completed')
+        return _('The task has been completed.')

src/pretix/presale/views/order.py

@@ -296,7 +296,7 @@ class OrderCancel(EventViewMixin, OrderDetailMixin, TemplateView):
         if not self.order:
             raise Http404(_('Unknown order code or not authorized to access this order.'))
         if self.order.status not in (Order.STATUS_PENDING, Order.STATUS_EXPIRED):
-            messages.error(request, _('You cannot cancel this order'))
+            messages.error(request, _('You cannot cancel this order.'))
             return redirect(self.get_order_url())
         return super().dispatch(request, *args, **kwargs)