Rework workflow documentation

The workflow documentation is a bit of a mess. Rework the documentation:

• Split the details out of the platform guide, making it a better high level overview of Apertis targeted more at selling the platform.
• Create an architectural document covering the basics of the Apertis workflow and how the tools used by Apertis fit together. Use pictures to help explain.
• Detailed information about workflows shifted to guides
  • Packaging guide starting to be restructured to better cover workflows by adding sections.
  • Separating out description of component repository layout into its own guide.
  • Shift image creation details to Image building guide.

While I've noticed:

• Packages have been moved from repository based sub-directories under pkg/ to pkg/ its self. Update the URLs used on the website to reflect this.

Signed-off-by: Martyn Welch martyn.welch@collabora.com