Tony Novak authored Sep 17, 2018 and Jonas Ådahl committed Sep 19, 2018

Previously, trackballs were detected based on the presence of the
substring "trackball" in the device name. This had the downside of
missing devices, such as the Kensington Expert Mouse, which don't have
"trackball" in their names.

Rather than depending on the device name, use the ID_INPUT_TRACKBALL
property from udev to determine whether or not to treat a device as a
trackball.

This adds a new function, `is_trackball_device`, to MetaInputEvents, and
eliminates the `meta_input_device_is_trackball` function.

Fixes: #258