Improve accessibility and move banner

[SVD-NL]

Accessibility changes

This site has not added much in terms of accessibility, i have added some elements to critical parts of the website:

• Add main and footer elements to allow for zone identification by tools such as screenreaders MDN Docs
• Change the menu from a div to a nav element, this allows various accessibility tools to identify it as a navigation menu Source
• Added alt text to the "latest" banner. Not 100% sure about this change, as the regular text does not indicate where it links to either.

This is by no means an extensive accessibility overhaul, but it is a good start.

Banner position

To optimize click-through and conversion rates, it is important to have a clear element indicating where the download page is.
In the current version, the banner is aligned with the viewport. This is fine for lower viewport widths, but when you open the website on a larger screen, it is quite far away from the main content. Personally i missed it completely (2560x1440):

In this PR i have moved the element into the same div as the logo/banner. I personally think this looks quite good, and doesn't look out of place.

Another option would be to create a new div aligned with the left bound of the main content.

These are just some small improvements i noticed when visiting the website, please let me know what you think, and if you'd like to see other changes.