Provide "kde" in the themeNames

KDE would like to get its integration plugin on Wayland.
The name won't change for Wayland, so filtering it out
because it is the name of the X11 desktop environment is
wrong.

The patch follows the approach of the QGenericUnixTheme.

Change-Id: Ia9c253ae6b5d609bd3bc630ce5c36b89811b079a
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>