New design to assessment page

[mfsilva22]

This updates the design of the assessment gallery, and brings the assessment text previously existing from inside the example course repo into the marketing page.

Still to be done:

• Decide if the images used for each assessment should be stored inside of each corresponding assessment folder, or at another common folder
• Learn how to add the images properly, once the location is defined
• Fix the links "Read more" and "try it now!" to the bottom of the assessment card, instead of at the end of the text.
• Learn how to use Latex
• Decide what to do with the comments for each question for each assessment example. I am inclined to add an image of the text. I don't think the current text/arrangement looks good
• Create component (?) which stores URL from PrairieLearn for the assessments. As of now, links to assessments are included in different files, and it may be useful to have these links all in one location, so that future updates are easier.
• Go over the text in each page, and make small improvements, fix links, etc
• Once this page is done, we should update the actual questions inside the PL repo, to replace the link to GitHub text with the new website (or no more linking)

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