Change MIME type and localStoragePrefix to 'font-' from 'x-font'. Fixes ...

[davidensinger]

...#1.

Per http://stackoverflow.com/questions/28235550/proper-mime-type-for-woff2-fonts and the comment from @theMikeD.

Not sure if you’d like to merge this, but this fix works for me too.

Thank you for your work on this :)