Add option to keep Drawer open

It would be useful to have an option to keep the Drawer control open.

Example scenario: When the mobile device is in portrait mode then the Drawer covers (almost) the whole screen and is closed (either by touching outside or when selecting an item).
When the mobile device is in landscape mode then the drawer covers only a small region and it might be useful to keep it open while the rest of the screen can be used for user controls.