Improved the transition into the statusbar

When expanding, the shelf now transforms into
the statusbar, providing a more seemless transition.

This also modifies the panel peeking:
previously the panel was always peeking right after a tap timeout
which would take the panel away from the users finger.
The panel is now only peeking when the user clicked on the bar instead.

Test: Add some notification and collapse the panel. Observe nicer transition
Bug: 32437839
Change-Id: I772f6684e1cee2004e9b366d203a5c5188af4a93