Update all, but one, <details> to component

Includes:

- in gulpfile.js:
  - add details macro to list of those copied from GOVUK Frontend
  - remove existing details polyfill
- convert all, but one, <details> tags to use GOVUK Frontend details component
- add jinja boolean filter to help setting 'open' attribute of <details> tags

Notes on the `<details>` not included in this:

The `<details>` used for notifications items on
the API integration page is not possible to
reproduce with the GOV.UK Frontend macro so I'm
splitting the resulting work out into it's own
commit.

gulpfile.js

@@ -63,7 +63,8 @@ const copy = {
         'skip-link',
         'header',
         'footer',
-        'back-link'
+        'back-link',
+        'details'
       ];
       let done = 0;
 
@@ -143,7 +144,6 @@ const javascripts = () => {
     paths.src + 'javascripts/govuk/cookie-functions.js',
     paths.src + 'javascripts/cookieMessage.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/enhancedTextbox.js',