apps/versions/feeds: add pagination support for RSS version history

This fixes bug https://bugzilla.mozilla.org/show_bug.cgi?id=1070766 by adding a ?all option to the Version History RSS feed, that displays the entire history.

I had thought about enabling pagination but decided this was simpler, since even with pagination there is no easy way (for a crawler) to figure out "the last page", which is what I really need to fix https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=762310.
Very good point, using urlparams would make it easier to not care about the existence (or not) of other params. Also, regarding the `rel="self"` link, it's not clear from the [RFC](http://tools.ietf.org/html/rfc5005#section-3) what it should represent: the "canonical" url (without the pagination, as was done by the google reader api?), or the current paginated url.