Apply GOV.UK branding to Smart Answer visualisations

Puts the visualisation inside the GOV.UK header/footer, with standard
typography, buttons and grid. This is quite custom compared to the
regular Smart Answer Format layout, but this is quite an exceptional
page with different needs to regular formats.

* Add the Alpha banner, required a Slimmer update
* Add some basic styling for the visualisation page, required FET update
* Link back to the Smart Answer itself
Modularise the visualisation JS
Improvements to the graph appearance itself

Standardise colours and use gov.uk type in graph nodes, simplify by reducing the number
of backgrounds and colours going on
Improved orientation toggle, and use top-to-bottom as default

Make the copy and button more GOV.UK-y, human friendly and buttons as actions.

Switch to top to bottom by default as it works better inside the GOV.UK chrome and fits more graph shapes, usually