Add an indication of waiting duplicates in the menu

Hi,

Currently, whether there are some duplicates found or not, the menu entry for "Duplicates" look the same. It would be really useful in my opinion to have some indicator next to the menu entry if potential duplicates are found.

Typically, this could be a small badge with the number of potential duplicates, same as in Gitlab next to issues.

EDIT: Related, #77 (closed).