Fix starting notification daemon

When multiple notification daemons are installed, bus activation doesn't
work. So, just installing dunst is not enough, it needs to be started
explicitly. And for the same reason, systemd unit cannot be used,
because systemd refuses to load two units with the same bus name (even
if only one is started at the same time).

QubesOS/qubes-issues#8768

Author: marmarek

i3.config

@@ -296,6 +296,9 @@ for_window [instance="zenity"] floating enable
 # necessary to make sure transient vm's come up
 exec --no-startup-id $desktop_autostart
 
+# Start dunst explicitly, bus activation can't work if there are multiple providers
+exec --no-startup-id dunst
+
 #######################################################################
 # automatically start i3-config-wizard to offer the user to create a
 # keysym-based config which used their favorite modifier (alt or windows)