menu-item: Add get/set for PrefersNonDefaultGPU (#21)

Closes #21
2 jobs for !16 with issue-21 in 2 minutes and 13 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Build
passed #14827
build

00:00:46

 
  Distcheck
passed #14828
distcheck

00:01:26