Allow to add a prefix when generating voucher codes (#518)

src/pretix/control/templates/pretixcontrol/vouchers/bulk.html

@@ -10,8 +10,11 @@
         {% bootstrap_form_errors form %}
         <fieldset>
             <legend>{% trans "Voucher codes" %}</legend>
-            <div class="form-group">
+            <div class="form-group form-inline">
                 <div class="col-md-7 col-sm-12 col-md-offset-3">
+                    <input type="text" class="form-control input-xs"
+                           id="voucher-bulk-codes-prefix"
+                           placeholder="{% trans "Prefix (optional)" %}">
                     <div class="input-group">
                         <input type="number" class="form-control input-xs"
                                id="voucher-bulk-codes-num"

src/pretix/control/views/vouchers.py

@@ -278,10 +278,11 @@ class VoucherRNG(EventPermissionRequiredMixin, View):
         except ValueError:  # NOQA
             return HttpResponseBadRequest()
 
+        prefix = request.GET.get('prefix')
         while len(codes) < num:
             new_codes = set()
             for i in range(min(num - len(codes), 500)):  # Work around SQLite's SQLITE_MAX_VARIABLE_NUMBER
-                new_codes.add(_generate_random_code())
+                new_codes.add(_generate_random_code(prefix=prefix))
             new_codes -= set([v['code'] for v in Voucher.objects.filter(code__in=new_codes).values('code')])
             codes |= new_codes