Disable "You are now offline" notifications

[lenemter]

Fixes #145

[TomiOhl]

Hmm it might be only me but I've disabled these once and had to google to enable them again.
Iirc this notification has a "Don't show again" button, so imo if anyone is bothered, they can just click it once and never again
Also the issue is rather about the case when the wifi is disabled by the user but would like to keep the notification for the case when the connection is lost for any other reason

[danirabbit]

@TomiOhl can you open a feature request against the network indicator to add an option to send network disconnected notifications? I think regardless we need to send them there and disable these so that we don't send them when a person disconnects manually

[TomiOhl]

Sure Danielle, opened elementary/wingpanel-indicator-network#313