[bug 810448] translate l10n properties into html markup

This patch generates markup for html pages that incorporates the locales data as a javascript dictionary in the markup.  This allows Margaret's changes (https://github.com/leibovic/gaia/commit/b8264cc4b49ae8d1fae0c35f9de04c2eb76be045) to have data to read.

This change depends on Fabrice's bug [811540](https://bugzilla.mozilla.org/show_bug.cgi?id=811540) and Margaret's change to be useful, but is safe to land before those.

I'm happy to answer any questions about the code and/or approach.  I'm pushing here because this is a great place for code review.