Fix relative url for notes.js

[SWW13]

The url for notes.js doesn't use the $reveal_location and therefor doesn't work for relative paths.

[joshed-io]

Thanks for the PR @SWW13. The notes plugin has an HTML file dependency that breaks CDN loading for some CDN's, hence why this is always pointed locally. But this isn't a great solution as it causes the problem you point out, so let me see if we can support both cases.