HomeScreen: Adding a config to adjust background of menu window

HomeScreen: Adding a config to adjust background of menu window

Currently, the backgrund of menu window is a white transparent
rectangle. If some windows are in application layer, we could
see this app window from menu window. So the menu window
looks mess and seems something wrong in layer management.

This patch add a config to adjust the background of menu window.
If background set to picture, the menu window won't be
transparent, then APP windows won't be seen from menu window.
If background set to transparent, nothing will change.

Change-Id: I8ae049344ac2d87e0a27bb7b829d70b9b04faddf
Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>