SystemUI: Move statusbar container object

The original ICS themeing code had the statusbar container (to rebuild
the views when switching themes) in the SystemUI service itself, since
it was the only common point between the phone and tablet bars.

JB introduced a BaseStatusBar class from which both layout types
derive, so move the container (and its initialization) there.

Additionally, explicitly make the phone statusbar view grab the input
focus when the window is expanded, to avoid missing the BACK keyevent
that makes it collapse.

Change-Id: I949bbf2087620406b1a2c91cf2ef8e91cf97bf32