[patch] Minor shutdown message grammar fix

I'm surfacing to offer this minor patch to update the shutdown messaging in the tray menu and various dialogs to use the two-word "shut down" when the message context is a verb rather than the one-word noun usage "shutdown".

For context, see:

* https://blogs.msdn.microsoft.com/oldnewthing/20060912-03/?p=29773/

* https://crowwriter.com/2017/11/27/two-or-one-words-spelling-rules/

Apologies for being the grammar nitpicker, but it's my forte. :-)

Best,

Anthony