Make sure slashes in JSON content don't end script tags. PLAT-462

The string "</script>" in JSON data would end the script element we're
embedding the data in.  To make sure the data doesn't disrupt the
script, we escape the slash as \/ .

common/templates/xblock_wrapper.html

@@ -1,5 +1,5 @@
 <div class="${' '.join(classes) | n}" ${data_attributes}>
-% if js_pass_parameters:
+% if js_init_parameters:
   <script type="json/xblock-args" class="xblock_json_init_args">
     ${js_init_parameters}
   </script>