Add visuals section

[edwardchalstrey1]

This is a draft PR that should be updated later for closing #51

It adds a "slideshow" feature for visuals, which can easily be extended to as many images as you want, and should look alright with images of different sizes/formats (within reason). The images cycle through the slides every few seconds

@tturocy To update this look right with the images (and section title) you want, you can simply update the config.yaml visuals section:

visuals:
      title: "Visualisations"
      interval_seconds: 5
      slides:
        - image: visuals/kuhn-4-card.svg
          caption: "Extensive form representation of a 4-card Kuhn poker game, illustrating information sets and strategy nodes."
        - image: visuals/test_image.jpg
          caption: "Placeholder image — replace with a screenshot or diagram from Gambit."

To do:

• Replace images
• Add footer for each image
• Change section title to something better than "Visualisations" (or remove)

Reviewers

Check out this branch and run the website locally in the usual way: https://github.com/gambitproject/gambitproject.github.io#developers

[tturocy]

Rahul and I had a look - we were thinking that instead of a carousel/slideshow that something more static like the row of visualisations at the top of Seaborn's page (https://seaborn.pydata.org) would maybe be a bit simpler? Again we'd imagine realistically just having a row of three or four images.

Our thinking in part is that a single row with all visible is useful because our visualisations are all quite different - we might have a game tree but then also a plot of empirical data, and with a slideshow someone might never notice the second (and subsequent) images rather than having them all laid out. And we'll never have so many that we'd really need to have them rotate live on the page.

[tturocy]

Yes, I like this much better. Suggested tweak would be that let's have the caption be a tooltip on mouseover rather than always be there - the hope is that many users will recognise what these are (it loses something if you have to explain it I think!).

Would be useful if the mechanism we've got for such a tooltip does allow us to link (for example we might want to link to a tutorial or demo that produces a version of the same image). I remember some ways of doing this in Bootstrap limit the ability to embed HTML in what pops up which is why I make the point of asking...

@rahulsavani image here for your convenience