Make sure we preserve UTF-8 from l10n.js to the watchface

It seems that somewhere on the way from l10n.js to the javascript code, something converted the translations from UTF-8 to ascii, which failed to be displayed on the pebble. So I have made sure we double encode the translations, and the handle the decoding in the preferences.c 
This solves the problem, and I'm able to see the translations again on android. Please test this on iOS and see if it works there too. 
Note: Don't forget the changes in the preferences.html I have.