Add inverse option for organisation logo

[andysellick]

What

Adds an inverse option for the organisation logo component.

This is currently WIP and limited to one organisation. Since organisations have different logos, rolling out a universal inverse option would require inverse versions of every logo.

Why

Part of some requirements.

Visual Changes

[matthillco]

I just noticed this PR and thought I'd comment with a possible quick solution for the inverted icons. We might consider using filter: invert(1) (or background-blend-mode: difference) for the icon. When a black icon is placed on a black background, these rules will make the icon appear white. Both of these are available for our target browsers. However I appreciate this might be considered a bit of a hack.

[JamesCGDS]

Thanks for the suggestion @matthillco - I ended up using a variation of this (filter: filter: brightness(0) invert(1);) because filter: invert(1) was also inverting the white link text, making it black. Adding brightness(0) seemed to resolve things though.

[AshGDS]

Looks good, had a few questions, and would need a changelog entry 👍

[JamesCGDS]

Thanks for the review @AshGDS 👍 Have addressed the comments and added a changelog entry - ready for a re-review when you get a mo

[AshGDS]

LGTM 👍