Improve screenshots / images on new site

[sagehrke]

• Find a more impressive image for the top of the page. Maybe a screenshot of a big schema?
• Under "Model" maybe we adapt box 1 ("Define Schema") of Figure 2 in our publication to go here.
• Remove the "FAIR" image. It's not needed. Or, use Figure 6 from our publication.
• Under "Generate" does this image say what we want?
• Under "Publish" update the image to show a mermaid diagram of a linkml Schema.