dbus: include dbus-launch in the main dbus package

dbus: include dbus-launch in the main dbus package

Followed suggestions from Bugz 2261:

2) make the virtual/libx11 DEPENDS conditional based on the x11 distro feature.
This makes the build dependencies reflect the feature list.

3) remove dbus-x11, meaning that dbus-launch with its potential X11 dependency
is now back in dbus where is belongs.

4) make dbus provide dbus-x11, for compatibility.

Fixes [Yocto #2261]

Signed-off-by: Radu Moisan <radu.moisan@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>