Bring back "Last seen date" filter#37

We used to be able to filter translations by last seen date in the dashboard. Now we can only sort them by last seen date. Filtering translations by date is super useful to clean up the database from translations that are no longer on the website.

For example, we used to be able to filter translations by “1 month or older”, select all matches and delete them to quickly get rid of all outdated translations. With sorting, this is also possible, but much more cumbersome and less convenient.

тЖрЩ