Translate: Classes section (7 articles)

[EpicHigh]

Part of #1

Translated

• 1-js/09-classes/index.md
• 1-js/09-classes/01-class/article.md + 1 task
• 1-js/09-classes/02-class-inheritance/article.md + 2 tasks/solutions + .view
• 1-js/09-classes/03-static-properties-methods/article.md + 1 task/solution
• 1-js/09-classes/04-private-protected-properties-methods/article.md
• 1-js/09-classes/05-extend-natives/article.md
• 1-js/09-classes/06-instanceof/article.md + 1 task/solution
• 1-js/09-classes/07-mixins/article.md + head.html

Total: 18 files (7 articles, 5 tasks, 4 solutions, 1 index, 1 .view)