ShellApp: Change activation API

Since almost all of the callers of shell_app_activate were using the
default workspace (by passing -1), remove that parameter.

Add a new shell_app_activate_full() API which takes a workspace as
well as a timestamp; previously we might have been ignoring event
timestamps from elsewhere.

https://bugzilla.gnome.org/show_bug.cgi?id=648149

js/ui/dateMenu.js

@@ -200,7 +200,7 @@ DateMenuButton.prototype = {
         this.menu.close();
         Main.overview.hide();
         let app = Shell.AppSystem.get_default().lookup_setting('gnome-datetime-panel.desktop');
-        app.activate(-1);
+        app.activate();
     },
 
     _onOpenCalendarActivate: function() {