Don't activate newly added workspaces

With workspace thumbnails, we want to make workspace switching
something that happens largely under the users control, so don't
switch to newly added workspaces in the overview.

https://bugzilla.gnome.org/show_bug.cgi?id=640996

js/ui/workspacesView.js

@@ -234,7 +234,6 @@ WorkspacesView.prototype = {
         } else {
             let currentTime = global.get_current_time();
             ws = global.screen.append_new_workspace(false, currentTime);
-            ws.activate(currentTime);
         }
 
         return ws;