ELECTRON-549: support not quitting app on mac upon closing window (#394)

js/main.js

@@ -169,7 +169,9 @@ app.on('ready', () => {
  * In which case we quit the app
  */
 app.on('window-all-closed', function() {
-    app.quit();
+    if (!isMac) {
+        app.quit();
+    }
 });
 
 /**

js/windowMgr.js

@@ -289,7 +289,9 @@ function doCreateMainWindow(initialUrl, initialBounds, isCustomTitleBar) {
             e.preventDefault();
             mainWindow.minimize();
         } else {
-            app.quit();
+            if (!isMac) {
+                app.quit();
+            }
         }
     });