[Application][Linux] Make '/running' a D-Bus object manager

This patch adds the D-Bus object representing a running application (at
the moment Crosswalk supports only one at a time). A running application
will export a Terminate() operation.

The patch makes sure that the cycle Launch -> Terminate works,
correctly, even if by non-ideal means. We'll fix as Crosswalk
application/ support is being reworked.