Finish storage wizard theming.

Storage wizard screens now have updated assets from UX, and various
assets are tinted consistently.  We're using our own navigation bar
and wholesale replacing the layout from upstream.

Fix text colors in night mode.  Tell SystemUI when we're finished
with the wizard flow.

Bug: 21830731
Change-Id: Ic8d09cc152bfb4dcc6089b5c61d28cbdd4be3ee9