Restructure projects into aspects and products

The menu should be restructured so it reflects the concepts of aspects and products.

"Aspects" (Aspekte) are the different topical pages that are already there.

"Products" (Produkte; maybe yet to be renamed) are concrete, publicly advertised things coming out of one of the projects. Currently, our products are AlekSIS and, depending on how we define it, Hack'n'Sun and FrogLabs.

Products get an external website, and should be linked from the website menu. The product links should be visually separated from the aspect links.