Fix #5530: checkout form error messages not translated in production

`frontend/views/spree/checkout/edit` included `jquery.validate` localization file past the asset pipeline, via `<script src="...">` tag. This resulted in messages not being translated to the user, because the requested script was not found when assets compilation was on.

Initially, I was going to fix only this issue, but as I started working on it, more stuff asked to be fixed.

Localization files were both in `core/vendor/assets/javascripts/jquery.validate/localization/` and `frontend/vendor/assets/javascripts/jquery.validate/localization/`. I merged them all to `frontend`, because `jquery.validate` appears to be used only there.

Those in `core/` had region suffixes added by a different rule and thus couldn't be reached by call from `checkout/edit` at all, even without precompilation: e.g. `messages_pt_BR` instead of `messages_ptbr`. I fixed this, overwriting older files when collisions happened.

Some files had wrong language code, like Ukrainian, Chinese (these two actually had both wrong and correct ones in different places) and Malay. I replaced them with ISO 639-1 codes.

And finally regarding the issue #5530, I replaced the script tag with a Sprockets method `javascript_include_tag`, which respects compiled assets, and added the file to `precompile` list in the engine's initializer. It includes only one translation for current default locale. Multilingual applications should add translation file for each of their available locales, like so (example for spree_i18n gem):

    Rails.application.config.assets.precompile += SpreeI18n::Config.available_locales.map do |locale|
      "jquery.validate/localization/messages_#{locale.to_s.gsub('-', '').downcase}.js"
    end

Build script ran without errors, but for now I lack expertise with phantomjs to add regression test for this bug and didn't knew if it is neccessary at all — adding another 5 seconds to a test suite for such a minor thing.