Support multi-selection in filtering

[lighterowl]

Multi-selection should be supported in filters by matching any element of the selected subgroups (statuses, folders, trackers, labels) and ANDing those expressions.

For example, selecting Downloading and Active in statuses, foobar in folders, mytracker1.org and mytracker2.org in trackers, and a, b and c in labels should show all torrents that :

• are either in Downloading or Active states,
• and their destination folder is foobar,
• and they're using either mytracker1.org or mytracker2.org,
• and they were assigned any of a, b, c labels.

[btTeddy]

This would be absolutely amazing if can be extended to trackers as well. One of the functions I have never seen on any other torrent client