Fixing several layout issues.

- N7/N9 indented area should not block scroll view
- separator at the end of the widget cell should not show up on the last item.

Not covered in this CL:
- Guarantee that last item is showing only 20~40%. Right now, the
hand picked constant works for N5,6,7,9

b/20338324
b/20763871

Change-Id: I274ab95c6c3e2fc8be8ceafb2e8172c0174a41a5