Bug 922463 - Part 1: rewrite build/multilocale.py in javascript
Bug 922463 - Part 2: Modified httpd extension for multilocale.js

use new build module "multilocale" to handle localization in httpd.js
extension because we no longer to push all l10n files into gaia,
meanwhile we need to handle http requests for l10n files.
Merge pull request #13135 from yurenju/multilocale.js-2

Multilocale.js 2 r=@timdream r=@ochameau r=@Pike