Rework structure, as of VC 2022-02-11

• updated entries in hamburger menu
• page stubs for how-to, use cases, mission
• take out green box from faq, create own mission page stub
  • Resolve endless redirect error at /mission
• make faq questions extendable
• howto use button on first page
  • stub for corresponding how-to page
• 4x services pages
• coarsely unified tutorials+materials page (?)