Fix locale-related issues.
  Renamed en locale to en-US (previously done during packaging).
  Added moz.build for integration with the Firefox build process.
  Enhanced the import-translations.sh script to omit incomplete locales
    and to generate jar.mn and chrome.manifest.
  Removed checking for incomplete locales from the pkg-prepare make target.
  Improved the output generated by import-translations.sh and pkg-prepare.