Always focus first when window is shown unless something already has focus.
Ensure Box preferred size is > 0
Add visible property to Widget
Add insert_before method to container
Add MessageDialog
Make Button border_radius default = 3
Make OnScreenKeyboard cursor start at end of text

This way backspace it useable immediately and it is probably more expected by the user anyway.
Change push_ and pop_window to show_ and close_window.

show_window works the same as push_ did, but close_window allows you to specify the window to close
instead of closing the top window.
Fix memory leak in Notebook.
Fix memory leak on DemoWindow Dialog demo