Fix icon size for Data Usage / Battery Stats / Process Stats

- remove padding from app_percentage_item and apply it correctly
on its containers
- wrap app_percentage_item into preference_app_percentage for having
correct padding o nProcessStatsPreference and PowerGaugePreference

Change-Id: I290c92959f51a33a1edb49435cd0bd1e6cd9afa3
7 files changed