Fixing overscroll effect when the navigation bar is opaque

The navigation bar is opaque on mobile devices in landscape mode.
Launcher should ignore the right insets and draw the edge effect appropriately.
Also draw the black bar under the navigation bar, just in case we assume it
to be opaque, but it was not actually opaque.

Bug: 18526657
Change-Id: I1d49dcb82b8a5ee25009bc738cd9b8c0c5c88263