[Application][D-Bus] Add the concept of an Running Application Object

This object will be used to keep track of running application lifetimes
and on later commits to follow the launcher bus name, so when it exits
the bus the applications is automatically killed.
[Application][D-Bus] Follow the xwalk-launcher D-Bus name

When the process that called Launch() on 'org.crosswalkproject.Running.Manager'
(typically xwalk-launcher) exits the bus (usually meaning that it was killed by
some kind of task manager) we need that the launched application also to exit.

We keep listening for the 'NameOwnerChanged' signal for the sender of the 'Launch()'
and when we receive a signal for that sender, with an empty new value (signifying
that there's no one with that name) we kill the application.
[Application][D-Bus] Only allow the launcher of the application to call Terminate()

We don't want other processes to kill others' applications, so we restrict the
calling of Terminate() to the process that caused the application creation.