You can no longer open a whole stack of Prefs windows, or Create Torrent windows
Simplifies and fixes behavior when dropping files onto the app or the dock icon. Before, you could use drag-drop to create stacks of Create Torrent windows. Now, you can only create torrents from the home screen.
Fixes#665
Less code for us to maintain.
This also gives us free internationalization in a future Electron
version (they'll set the label dynamically based on the 'role')
One slight regression with this change, but it will be fixed in a
future Electron once this PR is merged:
https://github.com/electron/electron/pull/6600
