Implement support for scroll button locks

Add a boolean option/property to enable/disable the scroll button lock. Where
enabled, the button can be clicked and released as opposed to having to be
held down.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
2 jobs for wip/scroll-button-lock in 1 minute and 1 second (queued for 1 second)
Status Job ID Name Coverage
  Containers Build
passed #730977
container_build

00:00:25

 
  Build
passed #730978
fedora:30@default-build

00:00:35