Bring back use of arrow keys for navigating folders

[Puglifiled]

Prior to the latest greatest release (1.0.80.474.gef6b503e) we could conveniently use the arrow keys to step through and open/close folders. It was a really really neat feature that someone decided we didn't want anymore. I see we can still step through playlists with the up/down arrow keys but not folders. So sad.

Edit 2018-06-05: Thanks for bringing back (fixing) arrow-key navigation on folders. Happy again.