Update HIG images with examples using OS8 stylesheet

[zeebok]

Problem

The images being used in the HIG are quite old. Not entirely useless but notably do not match the current styling of eOS

Proposal

Replace the images with fresh new ones!

Prior Art (Optional)

No response

[zeebok]

Might be good to take time to assess if there are any places that would benefit from adding images to them as well!

[wpkelso]

I think it's worth linking some images -- primarily those on the iconography page -- directly to the files they reference so we don't have to propagate changes whenever updates are made.

Looks like we might already be doing this, just haven't merged the PR to update the submodule