Improve performance of PDF page number counting

We were using PDF::Reader, a pure-ruby PDF parser to do this. Some
complex pdfs took up to 1 minute to parse some PDFs at full CPU usage[1].

The pdfinfo binary which is part of poppler-utils takes about 90ms to do
the same job.

[1] https://www.pivotaltracker.com/story/show/44095427
Use right-to-left stylesheet if chosen locale is right-to-left
Make requests for missing world location translations respond with 404
Provide locale-specific world location titles.

It's not possible to automatically translate a phrase like
'UK in France' into each locale. Instead, we should store the
translation along with the rest of the translated world location
content.
Add locale for Chinese
Translation migration needs locally scoped WorldLocation class

Without this, the migration fails against a dump of the production
database due to subsequent changes in WorldLocation.
Fix failing PDFInfo tests

/usr/bin/true is /bin/true on Linux systems, so we should use a
fake/stubbed executable path instead.