Update home page so that illustration shows on mobile view

[frankieroberto]

@paulrobertlloyd:

[the homepage needs] some custom markup and styles, to deal with the mobile behaviour of the illustration, which should always be anchored to the bottom of the container.

Originally posted by @paulrobertlloyd in #66

(This was the original behaviour, but we lost this when switching over to the Eleventy plugin)

[frankieroberto]

@paulrobertlloyd I wonder if this ought to be an option on the Hero component and/or product page layout?

Seems like theres’s a variety of behaviours out there...

Illustration hidden on mobile:

• GOVUK Notify
• GOVUK Forms
• Planning data

Illustration shown on mobile:

• GOVUK Pay
• GOVUK Wifi

🤷‍♂️