Redesign the landing page

[kysrpex]

We are taking too little advantage of the landing page of the docs, it is not helping the user at all.

I checked a few projects, and some of the best examples that I saw on how to make a good landing page are pandas or AiiDa. They just help you decide very quickly where do you want to go. rdflib also does it similarly, it is just not as eye-catching.

We would not lose anything relevant, as the index is already on the left-hand side of the website, and the compatibility matrix is not really necessary (see issue #79).

[pablo-de-andres]

I believe some of those examples are achieved with the sphinx panels extensions.
Probably worth looking into it.

[harrytodorov]

And to append a bit to @kysrpex's comment: it will be nice to have 1-2 sentences describing SimPhoNy (the text from the About section seems a quite nice fit for that)

[yoavnash]

/cib

[create-issue-branch]

Branch 78-Redesign_the_landing_page created!