[Applications][D-Bus] Add the concept of a D-Bus running application

This running Application object contains the logic of following the xwalk-launcher process (that caused this application to run) lifetime, the purpose of this is to terminate the Application when the launcher process exits. This is necessary for Tizen because its Task manager will only know the launcher process.

And as a precaution, a check for only allowing the launcher process to terminate the application (via the Terminate() call) is added.