Cached components may break after new styles deployed

[fofr]

We stumbled on this after #1117 and #1119 and had to implement fixes we later reverted in a follow up deploy like #1120.

If we modify both HTML and styles for a component in a deployment a quirk of caching means that the styling and markup can get out of sync. We saw this on govenrment-frontend.

It happens because:

• an app caches calls to components, creating a cached version of the template
• when a new static deploy is released we update the styles and the templates
• when the page cache expires, a new page is returned with the updated static styling
• BUT: the component may still be cached, so the new page ends up with new styling and old HTML
• when that cache expires, eventually a new page with new component template and new styles is returned

For a PR like #1119, if we hadn't caught this then for a period of ~15 minutes any users hitting a page that was cached with new styles and old component templates wouldn't have correctly styled titles.

Screenshot of the problem with pagination:

[tijmenb]

This has been solved by moving all components into the gem.