ui UI includes optional selection of download directory

[tangbrav]

1. Add to UI ability to select the target directory of the torrent download on the main BitTorrent page.  Place dropdown for directory specification to right of "Add Feed" as "optional Add Directory"

2. Currently this capability exist via:

> BitTorrent > Preferences > Directories > Put new downloads in: > selector for directory

-OR-

> BitTorrent > Preferences > Directories > Move completed downloads to: > selector for directory

3. The ability exists to specify the download directory.  However, this must be specified for each specific torrent

BitTorrent v 7.4.3 (43797) on macOS v Sierra v 10.12.6

Thank you,

t