shell: Send Quit() to the rebinder on SIGINT and SIGTERM
shell: Send Quit() to the rebinder on SIGINT and SIGTERM

Even when killing the application with one of those signals, we should
try to cleanup the mess we have by sending Quit() to the DBus processes
we launch.

Fixes: https://github.com/media-explorer/media-explorer/issues/30

media-explorer/media-explorer,media-explorer/media-explorer,media-explorer/media-explorer,media-explorer/media-explorer