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/ipc.js

@@ -69,6 +69,28 @@ function init () {
     menu.onPlayerClose()
     shortcuts.unregisterPlayerShortcuts()
   })
+
+  // Capture all events
+  var oldEmit = ipcMain.emit
+  ipcMain.emit = function (name, e, ...args) {
+    // Relay messages between the main window and the WebTorrent hidden window
+    if (name.startsWith('wt-')) {
+      var recipient, recipientStr
+      if (e.sender.browserWindowOptions.title === 'webtorrent-hidden-window') {
+        recipient = windows.main
+        recipientStr = 'main'
+      } else {
+        recipient = windows.webtorrent
+        recipientStr = 'webtorrent'
+      }
+      console.log('sending %s to %s', name, recipientStr)
+      recipient.send(name, ...args)
+      return
+    }
+
+    // Emit all other events normally
+    oldEmit.call(ipcMain, name, e, ...args)
+  }
 }
 
 function setBounds (bounds, maximize) {