FEATURE: Adds content for neos 8.3 release

[markusguenther]

• Adds the new 8.3 release page
• replaces the key visual with the second place of the wallpaper voting

[markusguenther]

Content Page

Startpage

[markusguenther]

While reviewing with @ahaeslich we have spotted an issue in the blog list, caused by image cropping and the text of the prologue was way too long.