layout: remove /changes/ (useless now)
layout: add link to /security/
core/layout: Add link to homepage source code on github
layout: Remove link to the list.

See also:
 https://groups.google.com/group/theslinux/browse_thread/thread/406ce2fcae1cda86
Merge branch 'core'
Add PGP public key for security@theslinux.org