Fix ImageView Padding and Margin issues

Fix ImageView Padding and Margin issues

- Currently padding does not apply to ImageView
  because the default Fitting Mode of ImageVisual have changed to FittingMode::FILL,
  so ImageVisual does not transform anything on ImageView::OnRelayout().

- Trigger to call Relayout when setting Margin and Padding.

- Removed SetBackgroundVisual() in control-impl.cpp as before,
  because it caused an incorrect behavior.

Change-Id: Ic9090180caec59dc5a5f0d63bbb95757f18be0ed
Signed-off-by: Seoyeon Kim <seoyeon2.kim@samsung.com>