abrt-configuration: read the ifaces from system dir

The standard directory for D-Bus interfaces is
/usr/share/dbus-1/interfaces.

The service recognizes the ifaces from their names. It considers all
files prefixed by 'com.redhat.problems.configuration' as the managed
iface.

Related to #750

Signed-off-by: Jakub Filak <jfilak@redhat.com>
spec: install configuration ifaces to the sys dir

Related to #750

Signed-off-by: Jakub Filak <jfilak@redhat.com>