Feat: locale generating adoption

Description

Resolve #2906 (closed)

Per upstream MR changed locale generation from Ruby to JS, thus the previous script we implemented will not be able to generate any locale file.

The current MR does two things to solve this problem

1. Add our Jihu own script to generate locale files: jh/scripts/frontend/po_to_json.js
2. Add jh/lib/tasks/gettext.rake to override Upstream's command gettext:compile

How to use

1. Manually delete the app.js file

   $ rm app/assets/javascripts/locale/en/app.js

2. Execute the command rake gettext:compile, expecting to regenerate app.js

   $ rake gettext:compile
   $ ls app/assets/javascripts/locale/en/app.js