Adding i18n/localization and static config option

[micschk]

• adds & sets language JS file Requirement based on i18n current locale (from CDN, exernal dependency)
• first day of week etc is also contained in language/locale files, so should be correct
• adds the standard SS Yaml based config system to allow setting default configuration options for flatpickr

@todo:

• could be extended to use contentLocale in front-end contexts to auto-include front-end i18n
• could be refactored to include & expose the locale/language files so they could be loaded locally instead of via CDN

Fixes #2

[micschk]

Just noticed the controllerextension also includes the requirements in the front-end, probably undesirable. Added a uniquenessID so the requirements can at least be blocked for now.

eg PageController::init():

            $userLangIso = i18n::getData()->langFromLocale(i18n::get_locale());
            Requirements::block("//npmcdn.com/flatpickr/dist/l10n/$userLangIso.js");
            Requirements::block("FlatpickrLocalization");