Save "Preview theme" option

[XhmikosR]

Not sure if it's worth doing this or not but it makes sense to have this saved via a cookie probably.

[hnrch02]

I'd opt for localStorage, much easier to work with than cookies and has surprisingly good browser support.

[XhmikosR]

I don't have any experience with that. I was think using jquery cookie to save the cookie, but if this is simpler and results in less code, I don't see why not using it 👍

[hnrch02]

Much less code, it's essentially just

localStorage.setItem(key, value);
localStorage.getItem(key, value);

[XhmikosR]

@hnrch02: PR is more than welcome :)

[hnrch02]

Incoming in ~2 hours.

[mdo]

Merged.