Onboarding screen with create account and sign in buttons.

Visual refresh of account creation and login interfaces.

Note: presently the onboarding will appear after each app
cold start. This is to allow easy testing. Will update
to only show one time once this patch has been signed off.

Pulled up the preview a bit on 3.5 inch screens.

Fixed issue with logging in through onboarding's create
account button sending user back to create account after
logging in.

Change-Id: I3c702292d8e26aa0f72e0eabeb04ae3cdebf2094