[build] [translation] Fix translation build error.

[swashata]

1. Update all gulp dependencies.
2. Use the new transifex API to push and pull files.

TODOS

• Add SaaS and JS build.
• Add extra files to export-ignore
  • All CSS .map files.
  • Source JS files (assets/scripts)
  • patches directory
  • gulptasks directory
  • .example.env file
  • CONTRIBUTING.md file
  • package-lock.json
• Compile all languages from the production source

NOTE FOR REVIEWER

• For now the transifex upload is protected against production. So if we try to upload to the production project, it will bail as a failsafe. I will remove this once @fajardoleo has confirmed that the translations (languages/freemius.pot) produced by the new system is good.
• I have removed the assets/js/nojquery.ba-postmessage.min.js file as now
  • The assets/scripts act as the source JS (uncompressed)
  • The assets/js acts as the build/compiled JS (compressed)
  • The PHP files enqueuing that script are also updated.
• While updating the SASS compiler, I fixed some SASS and autoprefixer warnings.