2.5 Toggle boxes should save

[matt]

The toggle boxes recently added to the write page should save state.

They should save the state in an asynchronous (and possibly batched on unload?) fashion, and save it as box_id + state.

When the page is loaded, it should add the "closed" class to those post boxes which are marked as such in the user's prefs. That way there's no delay and then redrawing, it's all built in to the CSS.

[nbachiyski]

Here is a patch, which saves in a cookie list of the id's of closed boxes and closes them on page load.

Since the cookie functions were already present in upload.js I took them out in cookies.js.

[nbachiyski]

This one saves the list of closed boxes in usermeta instead of in a cookie

[nbachiyski]

New patch, which saves the list of closed boxes in usermeta.

[lloydbudd]

Context for why cookie based solution discarded, matt:
"there's no reason to save it in a cookie. it's a permanent pref, not session or browser-based"

[ryan]

(In [6584]) Save toggle box open/closed state. Props nbachiyski. fixes #5610