Fix two pane widget picker bugs

Here we:
-Move no widgets text outside of the right pane so that we can center it
-setInset and change the clipping of children in the views so that we can fix the padding at the bottom when we have 3 button nav
-create selectedHeader where we keep track of the currently selected header in order to refresh the widgets for the selected header on rotation
-when widgets are bound we check if there are no recommended widgets, and if there aren't we select the first visible header

Fix: 324002996
Fix: 324001940
Fix: 323417968
Fix: 323460545
Fix: 323409306
Test: WidgetPickerImageTest
Flag: NONE
Change-Id: Ibd85cb086bb6c2aede6cf79da0c688a1fdaec4e5