Add ripple effect when a header in widget picker is selected.

We need to use setSelected in order to add a ripple effect when a header is selected in tablet landscape mode, and to set the style through XML rather than programmatically the way it was done before in the method `setLargeScreenTheme`.

Fix: 268558453
Test: Turn on LARGE_SCREEN_WIDGET_PICKER and verify that when selecting a header there's a ripple effect on that header
Change-Id: I6cab920258a57118430d1e07416508ef36faa56d