Reorder gov_cols

[mattkerlogue]

Suggest reviewing the order of the gov_cols palette so that when applied sequentially (rather than direct colour calls) on say a column chart there is suitable contrast/colour variation between columns.

[mattkerlogue]

Also, current configuration of check_pal() means that the colours rotate backwards in order from the quarter-past position. This might be confusing for users, who might presume that govuk_blue is the first colour (quarter-past being the only straight line) and colours sequence clockwise from there. Suggest this is amended if/when gov_cols is updated. Might also be good to show the hex codes to the colour labels?

[mattkerlogue]

Do we need graph_cols in addition to gov_cols to ensure maximum legibility/readability (thinking particular folk with colourblindness).

[mattkerlogue]

For reference:

• ONS Style advice on colours: https://style.ons.gov.uk/category/data-visualisation/using-colours/
• GOV.UK colour palette: https://design-system.service.gov.uk/styles/colour/ (current gov_cols vector doesn't match this palette).

Related to issue #7.