WebTorrent process

* Separate hidden window, with its own renderer process, for WebTorrent
  (Must be a window. You cannot run WebRTC at all in a Web Worker, and you can't
   run it well in a node process like the electron main process.)

* Disabled the create-torrent-modal for now. That gives us a consistent UX
  regardless of whether the user dragged files or folders onto the app or opened
  the Create New Torrent menu item.

* Main process routes all messages between the main and webtorrent windows.

* The renderer index.js is smaller now (but still too big), with the WebTorrent
  interface moved to webtorrent.js / it's own process.

* The UI should be faster now, and should not lag under load.

main/menu.js

@@ -124,7 +124,10 @@ function showCreateTorrent () {
     properties: [ 'openFile', 'openDirectory' ]
   }, function (filenames) {
     if (!Array.isArray(filenames)) return
-    windows.main.send('dispatch', 'seed', filenames[0])
+    var options = {
+      files: filenames[0]
+    }
+    windows.main.send('dispatch', 'createTorrent', options)
   })
 }