UX: Improve torrent status line

The goal of this commit is to merge the two torrent status lines onto a
single, concise line which has high signal and information density.

- Hide download speed, upload speed, and number of peers when 0,
because that's just noise.
- Remove number of files, because that information can be found by
expanding the torrent.

This also allowed the further reduction of the torrent item height from
110px to 100px.

main/windows.js

@@ -80,7 +80,7 @@ function createWebTorrentHiddenWindow () {
 }
 
 var HEADER_HEIGHT = 37
-var TORRENT_HEIGHT = 110
+var TORRENT_HEIGHT = 100
 
 function createMainWindow () {
   if (windows.main) {