Add Galician translation

Add Galician translation for 3a762c3cf91d6f65a5bb19aeb2056afacd777c71
Add "gl" in module.exports
Add Locale_GL in strings-app.js
Add Galician language in nls/README.md
Change Copyright year in strings.js
Merge pull request #8226 from ivarcia/patch-1

Add Galician translation