Merge pull request #6619 from Zuhayr/dev-freeze

Dev freeze
Fixes #6620

Obstructive wall is now a more cooperative floor plate.
Air horn replacement

The default sound for announcements is now one which does not wreck headset users.
Merge pull request #6627 from PsiOmegaDelta/AnnouncementBeep

Air horn replacement
Merge pull request #6623 from PsiOmegaDelta/DoorWall

Fixes #6620
Fixes #6628
Fixes #6613 and #6492