Restructure existing guide to merge with the new one

Update and re-shuffle the existing parts of the apparmor.md guide
to merge the old guide with the new guide:
 - Update summary with new ref links.
 - Reused a few sections but rephrased and updated references.
 - Removed a few, no longer needed, sections.
 - Fix minor formatting

Signed-off-by: Andreas Elvstam Cantner <andreas.elvstam@se.bosch.com>