Slightly increase default non-touch-mode delegate paddings

Part of teams/vdg/issues#37.

This has a couple of advantages:
- Larger click targets; faster interaction
- Easier usability when using a touchscreen or 2-in-1 laptop not in
  the explicit touch mode
- Looks a bit better; items feel less crammed
- Helps us toward the goal of porting things away from
  RoundedItemDelegate, which increases consistency everywhere

The downside is slightly decreased information density for very long
lists. But I think that's an acceptable trade-off.