Rename property & function for background image of Control
Rename property & function for background image of Control

Update for following changes in dali-toolkit:
Control::Property::BACKGROUND -> Control::Property::BACKGROUND_IMAGE
Control::SetBackground()      -> Control::SetBackgroundImage()
"background"                  -> "background-image"

Change-Id: I4fd1f14509fd14112bfeb38d0f18128b0f61ab2b

dalihub/dali-demo,dalihub/dali-demo,dalihub/dali-demo,dalihub/dali-demo