shell-app: Add "discrete_gpu" option when launching apps

And adapt existing callers to the new API. This will allow us to
implement a way to launch applications on the discrete GPU for systems
where an "Optimus" system exists.

https://bugzilla.gnome.org/show_bug.cgi?id=773117

js/ui/calendar.js

@@ -902,7 +902,7 @@ const EventsSection = new Lang.Class({
         let app = this._getCalendarApp();
         if (app.get_id() == 'evolution.desktop')
             app = Gio.DesktopAppInfo.new('evolution-calendar.desktop');
-        app.launch([], global.create_app_launch_context(0, -1));
+        app.launch([], global.create_app_launch_context(0, -1), false);
     },
 
     setDate: function(date) {