Scrolling doesn't work anymore inside a KVM/Spice virtual machine

Originally created by @alant on #7426 (Redmine)

In Tails 1.0 used as a KVM/spice guest (also qemu), scrolling using mouse wheel or equivalent works in the guest. It doesn’t work in 1.1.

Feature Branch: bugfix/7426-scrolling-in-Spice-VM

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