adds a button to the previous page, if there are no more tags on this page
If you're in the habit of wrangling bins backwards, from oldest to newest, you will have encountered this: You just wrangled all tags on, say, page 5, and the wrangulator refreshes to show you a cheerful message that there aren't any more tags. Now you'd have to manually change the URL, or select the "Unwrangled" bin and recreate your sorting, to continue wrangling on page 4.
This script gives you a handy link to the previous page that keeps all your sorting choices, so you can keep calm & carry on.
