Fix fragment widths on 10" tablet

- Add padding to edges of fragments
- Make list fragments more narrow on tablet landscape
- Make list / detail fragments 50/50 of the screen width
in tablet portrait
- Add divider to contact card with social updates
- Fix padding in group detail fragment header on tablet
- This doesn't cover 7" tablet, will come in later CL

Bug: 5082277
Change-Id: I31714cf633838a2d236c96720c1e70135f7bc74f