Feature: Windows. (#690)

Into ftxui/component/, add:
```
Container::Stacked(...)
Window(...);
```

Together, they can be used to display draggable/resizable windows.

Bug:https://github.com/ArthurSonzogni/FTXUI/issues/682

* Fix typo.

examples/dom/CMakeLists.txt

@@ -35,4 +35,3 @@ example(style_underlined_double)
 example(table)
 example(vbox_hbox)
 example(vflow)
-example(window)