Refactor and improve js_utils helpers

- Rename escape_json_dumps to dump_js_escaped_json
- Rename escape_js_string to js_escaped_string
- Update js_escaped_string to output empty string for None
- Introduce dump_html_escaped_json
- Move dump_js_escaped_json after the pipe as new best practice
- Introduce additional uses of helpers
- Introduce new djangolib directory and move js_utils

cms/templates/settings.html

@@ -8,7 +8,9 @@
   import urllib
   from django.utils.translation import ugettext as _
   from contentstore import utils
-  from openedx.core.lib.js_utils import escape_json_dumps
+  from openedx.core.djangolib.js_utils import (
+      dump_js_escaped_json, js_escaped_string
+  )
 %>
 
 <%block name="header_extras">
@@ -31,7 +33,10 @@ CMS.URL.UPLOAD_ASSET = '${upload_asset_url}';
 
 <%block name="requirejs">
     require(["js/factories/settings"], function(SettingsFactory) {
-        SettingsFactory("${details_url}", ${escape_json_dumps(show_min_grade_warning) | n});
+        SettingsFactory(
+            "${details_url | n, js_escaped_string}",
+            ${show_min_grade_warning | n, dump_js_escaped_json}
+        );
     });
 </%block>