* Add book "Essential Dart"

* Fix alphabetical order

* Update books/free-programming-books-langs.md
Co-authored-by: NImVector <59611597+LuigiImVector@users.noreply.github.com>
Co-authored-by: Njcreach <creach.0709@apside-groupe.com>
Co-authored-by: NImVector <59611597+LuigiImVector@users.noreply.github.com>