Add "new folder" option to location selection

[qstokkink]

When saving a torrent, I wanted to make a new directory inside of an existing one (example screenshot above). To do so, I had to open my file explorer and browse to the appropriate folder create it there and then select it inside Tribler. It would be nice to have a "create new folder" within the file browser.

[qstokkink]

As a workaround, simply setting the "Destination" (in the previous dialog) will create a folder that does not exist.