Using native file choosers whenever possible. cleanup.

 - Had to resort to a UX workaround as native looking FileDialogs
   don't allow for folder selection. Whenever files have to be selected
   we use the native dialog which is always much better. When folder
   selection comes we use the JFileChooser.

 - Don't go to Search Tab if you cancel opening a torrent on the library.

 - NPE fix.

 - Cleanup

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cleanup
Fixes bug where torrents made out of folders couldn't be seeded.
Merge pull request #283 from gubatron/file-chooser-updates

Using native file choosers whenever possible. cleanup.