Allow to set short uuids as default

[TheZoker]

Thanks for implementing my request for #295

Now that the shorter url can be used as an alias to the long one, it would be nice, if there was an option to show/use this short url everywhere where currently the long is used.

So in the name, the url, the embed etc.

Because I want to share the gist with other users I now have to always count the chars for the short url to use it and remove the others from the url when I share it.

Thanks!