Stop using Babel to transpile gulpfile

Bumping NodeJS to 10.15.3 removes the need to
transpile `gulpfile.js` as this version includes
all the ES6 features used..

Also removes .babelrc file. This was included to
ensure the gulpfile was transpiled correctly so it
is no longer needed.

gulpfile.js

@@ -0,0 +1,187 @@
+// GULPFILE
+// - - - - - - - - - - - - - - -
+// This file processes all of the assets in the "src" folder
+// and outputs the finished files in the "dist" folder.
+
+// 1. LIBRARIES
+// - - - - - - - - - - - - - - -
+const { src, pipe, dest, series, parallel } = require('gulp');
+const loadPlugins = require('gulp-load-plugins');
+const stylish = require('jshint-stylish');
+
+const plugins = loadPlugins();
+
+// 2. CONFIGURATION
+// - - - - - - - - - - - - - - -
+const paths = {
+  src: 'app/assets/',
+  dist: 'app/static/',
+  templates: 'app/templates/',
+  npm: 'node_modules/',
+  template: 'node_modules/govuk_template_jinja/',
+  toolkit: 'node_modules/govuk_frontend_toolkit/'
+};
+
+// 3. TASKS
+// - - - - - - - - - - - - - - -
+
+// Move GOV.UK template resources
+
+const copy = {
+  govuk_template: {
+    template: () => {
+      return src(paths.template + 'views/layouts/govuk_template.html')
+       .pipe(dest(paths.templates));
+    },
+    css: () => {
+      return src(paths.template + 'assets/stylesheets/**/*.css')
+        .pipe(plugins.sass({
+          outputStyle: 'compressed'
+        }))
+        .on('error', plugins.sass.logError)
+        .pipe(plugins.cssUrlAdjuster({
+          prependRelative: process.env.NOTIFY_ENVIRONMENT == 'development' ? '/static/' : '/',
+        }))
+        .pipe(dest(paths.dist + 'stylesheets/'));
+    },
+    js: () => {
+      return src(paths.template + 'assets/javascripts/**/*.js')
+        .pipe(plugins.uglify())
+        .pipe(dest(paths.dist + 'javascripts/'));
+    },
+    images: () => {
+      return src(paths.template + 'assets/stylesheets/images/**/*')
+        .pipe(dest(paths.dist + 'images/'));
+    },
+    fonts: () => {
+      return src(paths.template + 'assets/stylesheets/fonts/**/*')
+        .pipe(dest(paths.dist + 'fonts/'));
+    },
+    error_page: () => {
+      return src(paths.src + 'error_pages/**/*')
+        .pipe(dest(paths.dist + 'error_pages/'))
+    }
+  }
+};
+
+
+const javascripts = () => {
+  return src([
+      paths.toolkit + 'javascripts/govuk/modules.js',
+      paths.toolkit + 'javascripts/govuk/show-hide-content.js',
+      paths.src + 'javascripts/stick-to-window-when-scrolling.js',
+      paths.src + 'javascripts/detailsPolyfill.js',
+      paths.src + 'javascripts/apiKey.js',
+      paths.src + 'javascripts/autofocus.js',
+      paths.src + 'javascripts/highlightTags.js',
+      paths.src + 'javascripts/fileUpload.js',
+      paths.src + 'javascripts/expandCollapse.js',
+      paths.src + 'javascripts/radioSelect.js',
+      paths.src + 'javascripts/updateContent.js',
+      paths.src + 'javascripts/listEntry.js',
+      paths.src + 'javascripts/liveSearch.js',
+      paths.src + 'javascripts/errorTracking.js',
+      paths.src + 'javascripts/preventDuplicateFormSubmissions.js',
+      paths.src + 'javascripts/fullscreenTable.js',
+      paths.src + 'javascripts/previewPane.js',
+      paths.src + 'javascripts/colourPreview.js',
+      paths.src + 'javascripts/templateFolderForm.js',
+      paths.src + 'javascripts/main.js'
+    ])
+    .pipe(plugins.prettyerror())
+    .pipe(plugins.babel({
+      presets: ['es2015']
+    }))
+    .pipe(plugins.addSrc.prepend([
+      paths.npm + 'hogan.js/dist/hogan-3.0.2.js',
+      paths.npm + 'jquery/dist/jquery.min.js',
+      paths.npm + 'query-command-supported/dist/queryCommandSupported.min.js',
+      paths.npm + 'diff-dom/diffDOM.js',
+      paths.npm + 'timeago/jquery.timeago.js',
+      paths.npm + 'textarea-caret/index.js'
+    ]))
+    .pipe(plugins.uglify())
+    .pipe(plugins.concat('all.js'))
+    .pipe(dest(paths.dist + 'javascripts/'))
+};
+
+
+const sass = () => {
+  return src(paths.src + '/stylesheets/main*.scss')
+    .pipe(plugins.prettyerror())
+    .pipe(plugins.sass({
+      outputStyle: 'compressed',
+      includePaths: [
+        paths.npm + 'govuk-elements-sass/public/sass/',
+        paths.toolkit + 'stylesheets/'
+      ]
+    }))
+    .pipe(plugins.base64({baseDir: 'app'}))
+    .pipe(dest(paths.dist + 'stylesheets/'))
+};
+
+
+// Copy images
+
+const images = () => {
+  return src([
+      paths.src + 'images/**/*',
+      paths.toolkit + 'images/**/*',
+      paths.template + 'assets/images/**/*'
+    ])
+    .pipe(dest(paths.dist + 'images/'))
+};
+
+
+// Watch for changes and re-run tasks
+const watchForChanges = () => {
+  return watch(paths.src + 'javascripts/**/*', ['javascripts'])
+    .watch(paths.src + 'stylesheets/**/*', ['sass'])
+    .watch(paths.src + 'images/**/*', ['images'])
+    .watch('gulpfile.js', ['default']);
+};
+
+const lint = {
+  'sass': () => {
+    return src([
+        paths.src + 'stylesheets/*.scss',
+        paths.src + 'stylesheets/components/*.scss',
+        paths.src + 'stylesheets/views/*.scss',
+      ])
+      .pipe(plugins.sassLint({
+        'options': { 'formatter': 'stylish' }
+      }))
+      .pipe(plugins.sassLint.format())
+      .pipe(plugins.sassLint.failOnError());
+  },
+  'js': (cb) => {
+    return src(paths.src + 'javascripts/**/*.js')
+      .pipe(plugins.jshint())
+      .pipe(plugins.jshint.reporter(stylish))
+      .pipe(plugins.jshint.reporter('fail'))
+  }
+};
+
+// Default: compile everything
+const defaultTask = parallel(
+  series(
+    copy.govuk_template.template,
+    copy.govuk_template.images,
+    copy.govuk_template.fonts,
+    copy.govuk_template.css,
+    copy.govuk_template.js,
+    images
+  ),
+  series(
+    copy.govuk_template.error_page,
+    javascripts,
+    sass
+  )
+);
+
+exports.default = defaultTask;
+
+exports.lint = series(lint.sass, lint.js);
+
+// Optional: recompile on changes
+exports.watch = series(defaultTask, watchForChanges);