Allow screen unpinning on devices without navbar

Change-Id: Iedfc08f4d95bbee3c8578c0d2450b90739e63603

Screen Pinning: Show correct text for on screen nav.

  Similar to I09c2ef661bff272cb4f7ca43bac0e45f4b20a4d4,
  we're not getting an instance of PhoneWindowManager which
  we can rely on to update dynamically.

  TICKET: OPO-393

Change-Id: Iacf8221066461fb6940dd88432e665812545c3ff