Docs website design update
Created by: twotribes
Since the main website has now published the new subsection with a large collection of TVB EduCases, we can link to them from the documentation website.
This PR introduces general links to TVB EduCases on the homepage and more specific ones in the GUI Guide (exemplary introduction lectures) and in the Tutorials (new subsection there with exemplary tutorial links for every covered topic).
Also, several outdated/broken links in the documentation website were fixed: they had pointed to supposed datasets on Ladeluke or GitHub. Now they're all pointing to the newest version of TVB's Zenodo dataset repo.
The Zenodo repo is now also mentioned and linked on the documentation website's homepage.