Don't reload page when re-sorting answers if we don't need to

[cellio]

meta:292886

When you change how answers are sorted on a question, we do a full page reload. This isn't a big deal in a lot of cases, but if you're on a slow network connection it can be painful. If all of the answers fit on the page, can we re-sort them without a full page load? (Presumably requires Javascript, and it's ok to say that if you disable JS, it falls back to the page load.)

If there are more answers than fit on the page (i.e. if pagination is already happening), client-side sorting isn't possible (the answers you need might be on other pages), so we should reload in that case. I don't know how hard it is to ask Rails "are you paginating?"; the calls to paginate seem to all take a number (not currently a const) as an arg, so I don't know how we can ask if answer count is greater than page size.