Try country-dependent jQueryUI localization files

When we load the jQueryUI, we should check if there's a file with full
locale code (eg ui.datepicker-zh-CN.js) before trying to load the file
with language-only code (eg ui.datepicker-zh.js).
Merge pull request #137 from mlocati/better-jqueryui-localization

Try country-dependent jQueryUI localization files