desktopGrid.js: Check shell version for method existence

In gnome shell 3.32 there was an API change, where the show() method was renamed as open(), and hide() as close(); thus the correct one must be called to ensure compatibility with previous versions.

In the previous patch, this was done just by checking the existence of the newest method, and if it didn't exist, the old one should be called. This is not a good way of doing it. The right way is implemented in this patch, by checking the current gnome shell version and calling the right method.