Get HTML LaTeX "working" again.

common/lib/xmodule/xmodule/html_module.py

@@ -19,6 +19,7 @@ log = logging.getLogger("mitx.courseware")
 
 class HtmlFields(object):
     data = String(help="Html contents to display for this module", scope=Scope.content)
+    source_code = String(help="Source code for LaTeX documents. This feature is not well-supported.", scope=Scope.settings)
 
 
 class HtmlModule(HtmlFields, XModule):