[Application][Linux] Expose interface for launch apps via D-Bus

The exported object '/running/' supports only one method in its
interface, that is used to Launch applications. The ObjectManager based
interface will come in future patches, once the notion of "running
application" is added to Crosswalk (Mikhail / Alex work).

At the moment, Crosswalk quits after the application window is closed,
even running as a service. This behavior will change in future
patches.