Notification when a command is completed

[plfiorini]

Send a notification when a command is completed.

[plfiorini]

Prior art:
https://discourse.ubuntu.com/t/adding-terminal-notifications-for-completed-commands-to-the-default-desktop/212/8
debarshiray/vte@7e42ecb
https://github.com/jml/undistract-me/blob/master/long-running.bash#L47-L54
https://bugzilla.gnome.org/show_bug.cgi?id=711059