Spike trying out globalize3 on edition title.

* We had to implement Edition#title_changed? method.

* We had to make use of the Edition#translations association (added by
globalize3) and its corresponding table, edition_translations, in order
to implement the Edition scopes that search for a title, and to avoid
N+1 query tests failing. Note that for a proper implementation we ought to further restrict such joins by the current locale.

* We had to rebase against the `remove-paper-trail` branch in order to get all the tests to pass, because of some nasty interactions between Globalize3 and PaperTrail.

* All tests are currently passing.