frontpage: move content from layout to content
Currently, when you press the "Edit this page"-button on the front-page, you get to a surprisingly empty page. This is because the whole page-content was hard-coded into the layout-file. That's not ideal.
Part of the reason it was written this way, is due to all the custom HTML in there, which isn't usually legal in Hugo markdown content files.
But instead, we can simply use a HTML content file as well as a custom shortcode for the latest news section instead, and everything just as intended. The custom partials we used for the apis and features subsections can be repurposed as shortcodes as well.
This makes this stuff more in line with how these primitives are intended to be used than what we used to do. And at the same time, we get a much more meaningful "Edit this page"-behavior than before.