Update gitignore and incluye all scaffold files

[jonhattan]

List of scaffold files in composer.lock. I guess this appropriate:

$ grep scaff composer.lock 
                "drupal-scaffold": {
                        "[project-root]/.editorconfig": "assets/scaffold/files/editorconfig",
                        "[project-root]/.gitattributes": "assets/scaffold/files/gitattributes",
                        "[web-root]/.csslintrc": "assets/scaffold/files/csslintrc",
                        "[web-root]/.eslintignore": "assets/scaffold/files/eslintignore",
                        "[web-root]/.eslintrc.json": "assets/scaffold/files/eslintrc.json",
                        "[web-root]/.ht.router.php": "assets/scaffold/files/ht.router.php",
                        "[web-root]/.htaccess": "assets/scaffold/files/htaccess",
                        "[web-root]/example.gitignore": "assets/scaffold/files/example.gitignore",
                        "[web-root]/index.php": "assets/scaffold/files/index.php",
                        "[web-root]/INSTALL.txt": "assets/scaffold/files/drupal.INSTALL.txt",
                        "[web-root]/README.md": "assets/scaffold/files/drupal.README.md",
                        "[web-root]/robots.txt": "assets/scaffold/files/robots.txt",
                        "[web-root]/update.php": "assets/scaffold/files/update.php",
                        "[web-root]/web.config": "assets/scaffold/files/web.config",
                        "[web-root]/sites/README.txt": "assets/scaffold/files/sites.README.txt",
                        "[web-root]/sites/development.services.yml": "assets/scaffold/files/development.services.yml",
                        "[web-root]/sites/example.settings.local.php": "assets/scaffold/files/example.settings.local.php",
                        "[web-root]/sites/example.sites.php": "assets/scaffold/files/example.sites.php",
                        "[web-root]/sites/default/default.services.yml": "assets/scaffold/files/default.services.yml",
                        "[web-root]/sites/default/default.settings.php": "assets/scaffold/files/default.settings.php",
                        "[web-root]/modules/README.txt": "assets/scaffold/files/modules.README.txt",
                        "[web-root]/profiles/README.txt": "assets/scaffold/files/profiles.README.txt",
                        "[web-root]/themes/README.txt": "assets/scaffold/files/themes.README.txt"