2.0.3: Standardize plugin scaffold format to align with template scaffold

- Drop unused requireLivewire from gp247.json and bump requireCore to 2.0
- Use gp247_language_render() for disable() error message instead of a
  hardcoded string, matching the template scaffold's i18n convention
- Split the bilingual readme.md into readme.md (EN) and readme_vi.md (VI)
- Remove empty public/css, public/fonts, public/js placeholder dirs