Add GOVUK Frontend to the frontend build

- copies across the images
- adds the Sass folder to the Sass include paths

JS is added file-by-file so will be added when
specific files are needed.

gulpfile.js

@@ -28,7 +28,8 @@ const paths = {
   templates: 'app/templates/',
   npm: 'node_modules/',
   template: 'node_modules/govuk_template_jinja/',
-  toolkit: 'node_modules/govuk_frontend_toolkit/'
+  toolkit: 'node_modules/govuk_frontend_toolkit/',
+  govuk_frontend: 'node_modules/govuk-frontend/'
 };
 
 // 3. TASKS
@@ -70,6 +71,12 @@ const copy = {
       return src(paths.src + 'error_pages/**/*')
         .pipe(dest(paths.dist + 'error_pages/'))
     }
+  },
+  govuk_frontend: {
+    fonts: () => {
+      return src(paths.govuk_frontend + 'assets/fonts/**/*')
+        .pipe(dest(paths.dist + 'fonts/'));
+    }
   }
 };
 
@@ -122,7 +129,8 @@ const sass = () => {
       outputStyle: 'compressed',
       includePaths: [
         paths.npm + 'govuk-elements-sass/public/sass/',
-        paths.toolkit + 'stylesheets/'
+        paths.toolkit + 'stylesheets/',
+        paths.govuk_frontend,
       ]
     }))
     .pipe(plugins.base64('../..'))
@@ -136,7 +144,8 @@ const images = () => {
   return src([
       paths.src + 'images/**/*',
       paths.toolkit + 'images/**/*',
-      paths.template + 'assets/images/**/*'
+      paths.template + 'assets/images/**/*',
+      paths.govuk_frontend + 'assets/images/**/*'
     ])
     .pipe(dest(paths.dist + 'images/'))
 };
@@ -192,6 +201,7 @@ const defaultTask = parallel(
     copy.govuk_template.fonts,
     copy.govuk_template.css,
     copy.govuk_template.js,
+    copy.govuk_frontend.fonts,
     images
   ),
   series(