Merge topic 'doc-3.13-relnotes'

00d96c51c9 Help: Organize and revise 3.13 release notes
2fd2c8cb7e Help: Consolidate 3.13 release notes

Acked-by: Kitware Robot <kwrobot@kitware.com>
Reviewed-by: Marc Chevrier <marc.chevrier@gmail.com>
Reviewed-by: Craig Scott <craig.scott@crascit.com>
Merge-request: !2426