Support product pictures for add-on products

src/pretix/static/pretixpresale/scss/_forms.scss

@@ -140,4 +140,9 @@
       flex-shrink: 1;
     }
   }
-}
+}
+@media (max-width: $screen-sm-max) {
+  .form-horizontal .control-label {
+    text-align: left;
+  }
+}