Centralize default style in `A0Theme`
Fix style for DB auth screens.
Fix auth form box styles.
Fix auth views nav buttons.
Fields icon & placeholder styles.
Update assets images.
Fix layout for 3.5" screens.
Resize icon container views to allow bigger icons.
Use A0Theme to customize touch id btn image.
Close button style.
Merge pull request #46 from auth0/chore-styleguide

Native widgets styles