Switch 7 inch tablets to single-pane preferences, like phones.

Move a bunch of dimensions around so that 7" tablets use phone-style
UI but with different margins to reduce the width.

24dp margin for portrait and 48dp margin for landscape.
Existing sw600dp values moved to sw720dp.
New sw600dp values created.

Bug: 6445803
Change-Id: I835c8f4b0423b295dd453161f4e32406e6267515