dbus: split -common and -tools out of main package
Certain config files and units are shared between dbus-daemon and
dbus-broker (available in meta-openembedded), so split them out to
allow installing dbus-broker without pulling in dbus-daemon and its
dependencies.
Stand-alone command line tools can also be used regardless of whether
the buses are provided by dbus-daemon or dbus-broker, so split them
out into dbus-tools.
Finally, move the XML schema files out of the main package and into
the development package.
All these changes follow the same pattern used by Fedora, which was
one of the first distro to switch to dbus-broker by default:
