added the date/time to recent downloaded items as tooltip

I've always been confused by the "recently downloaded torrents" menu item, because of two things:

1) I'm never sure how the items are sorted (1-10 doesn't make it clear). Newest on bottom? Top? What's the number for? 

2) Even if I knew how they were sorted, because I don't download much with Catch, I don't know how recent the most recent item is. Did it download today? Or a week ago?

So - this change is a start I guess. Solves my problem by adding a tooltip to the menu items to show the date/time of download. Could probably get a bit fancier later and have a preference that says how many days to display in the recent list, but that would require localization.