Add Ukraini dialog

[Falke-Design]

Replaces the existing Urkaini war site with an dialog.

With this change existing PRs don't get merge conflicts like #7818 and existing links, redirects are working again.
The dialog opens only once every 24 hours.

@mourner @IvanSanchez @Malvoz do you see any problems with the usage of sessionStorage and iframe?
The changed files for the dialog are:

• /SlavaUkraini/*
• index.html
• /_layouts/v2.html
• /docs/css/main.css

Here a demo. In the demo I changed that the dialog opens every 10 seconds again (on a site change).

[Malvoz]

The change to logo-ua.png is reverting @mourner's 3f22bb8.

Edit: it'd be neat to maintain the transparent background with the new colors though.

[mourner]

This looks great! I was thinking about moving it back to help with the conflicts, but the dialog idea is brilliant. 👍 from me apart from addressing things @Malvoz brought up.

[mourner]

Edit: it'd be neat to maintain the transparent background with the new colors though.

I thought about it, but it's only displayed on white background, and it actually looks better around the edges because the original logo source I have doesn't have proper transparency there, leading to some pixel artifacts. I think it's fine to keep it white bg.

[Malvoz]

Seems to work well, nice!