Rework licensing documentation

The licensing documentation is linked from the home page, but is a bit of a
mess, with guidance on documenting licensing and information about the Apertis
licensing scanning infrastructure mixed with Apertis licensing policies.

Split out the license scanning documentation into a separate architecture
document. Move the small amount of policy documentation from the applying
licensing document and move to guides.

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