Upgrade Linux to 4.18

linux-image-4.18.0-1-amd64 is now the default on sid so 4.17 (shipped in 3.9 and on current stable) won’t get any security upgrade anymore.

Feature Branch: feature/15936-linux-4.18-stable-bump-Debian+force-all-tests

Original created by @intrigeri on 15936 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information