Fixing navbar and notification shade overlap

Moving notifications scrim bottom edge a bit higher - according to the specs. That involved some collateral changes as bottom margin was never updated in NotificationsQuickSettingsContainer.
Also renaming resources:
notification_panel_margin_bottom -> notification_panel_padding_bottom
close_handle_underlap -> notification_panel_margin_bottom
which I think reflects a bit better what they're doing.

Fixes: 213304101
Test: manual + NotificationQSContainerControllerTest
Change-Id: I7102e01b98fc9f1298bd20c9d722706e85829d87