Fix screen stacking bug

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

src/renderer/views/update-available-modal.js

@@ -11,18 +11,18 @@ module.exports = class UpdateAvailableModal extends React.Component {
         <p><strong>A new version of WebTorrent is available: v{state.modal.version}</strong></p>
         <p>We have an auto-updater for Windows and Mac. We don't have one for Linux yet, so you'll have to download the new version manually.</p>
         <p className='float-right'>
-          <button className='button button-flat' onClick={handleCancel}>Skip This Release</button>
-          <button className='button button-raised' onClick={handleOK}>Show Download Page</button>
+          <button className='button button-flat' onClick={handleSkip}>Skip This Release</button>
+          <button className='button button-raised' onClick={handleShow}>Show Download Page</button>
         </p>
       </div>
     )
 
-    function handleOK () {
+    function handleShow () {
       electron.shell.openExternal('https://github.com/feross/webtorrent-desktop/releases')
       dispatch('exitModal')
     }
 
-    function handleCancel () {
+    function handleSkip () {
       dispatch('skipVersion', state.modal.version)
       dispatch('exitModal')
     }