Added basic support for multiple windows in windows 10

app/lib/window.ts

@@ -147,6 +147,10 @@ export class Window {
         this.window.webContents.send(event, ...args)
     }
 
+    isDestroyed() {
+        return !this.window || this.window.isDestroyed();
+    }
+
     private setupWindowManagement () {
         this.window.on('show', () => {
             this.visible.next(true)