Create iconography for about and now pages

[querkmachine]

These pages currently use system emoji for iconography. This is a lil unreliable (not all devices can show all emoji) and not necessarily accessible when it comes so colour contrast or screen reader announcements.

Ideally these would be custom icons akin to those used for webrings.

[querkmachine]

New icons for the about page were added in #300.

I'm not sure what's best to do about the now page, as the emoji used there tend to change over time. It might require formalising some categories first.