Add overlay noscript message to fix #6032

How about this as an alternative to #6193?:

![image](https://f.cloud.github.com/assets/127738/1683086/da9f18b4-5db7-11e3-8db6-011d1325c263.png)

The subdued red background is an overlay that prevents mouse access to the application.  The message informs of what needs to be done to re-enable regular operation.

Note that this seems to work on my Chrome 32, as in the screenshot.