Make StatusBar optional in NotificationClicker.

StatusBar is an optional component and some device may use notification
related components only.

The CL make StatusBar reference in NotificationClicker optional to allow
use NotificationClicker without StatusBar.

Bug: 143224715
Bug: 145962019
Test: Build and boot cheets target
Change-Id: I90fa5291bc47e8b95d7fe3cced2656d8aa55ba58