stop including ?q= in _item_link links: it's getting cached, so is almost always wrong
Move closet-hangers-update form from partial to JS

We lose no-JS support, which I kinda miss, but caching is gonna be more
important down the line. Delete form moves next, then we cache.

CSRF token changes: it looks like, by setting a data attribute in AJAX, I
was overwriting the CSRF token. I don't remember it working that way, but
now we use beforeSend to add the X-CSRF-Token header instead, which is nicer,
anyway. The issue might've been something else, but this worked :/

The CSS was also not showing the loading ellipsis properly. I think that's a
dev-only issue in how live assets are being served versus static assets, but
may as well add UTF-8 charset directives everywhere, anyway.
move closet-hanger-destroy form to JS
Move item_link partial caching to a helper rather than the template itself

This is a surprisingly huge performance gain. On my testing (with
cache_classes set to true to also cache templates), this sped up
closet_hangers#index rendering by a factor of 2 when there were a
significant number of items. Cool beans.

I think we can even hold off on the individual hanger caching now:
we've made the closet hanger partial tons faster by moving forms out
of them and doing this cache check earlier. I'm expecting significant
performance gains both here and on items#index (though less so there).
I'll deploy and see how much it helps in production; if not enough, we
can look at the layered caching of hangers, lists, groups, full pages,
etc.

So glad we don't *have* to move to a pagination model!
noscript warning on closet_hangers#index