Pass additional props to ScrollView, fix circle proptypes

[adbl]

• Passes any additional props down to the ScrollView. I needed this to add style and can add a special property for that if that's more appropriate, note that wrapperStyle didn't work in my case since I needed to set overflow: visible on the scrollview.
• Fixes passing StyleSheet styles to the circle props without warnings.
• Don't render items before onLayout. Fixes layout issue where flex text (sub) children would not wrap if they where first rendered without bounds.

Based on the fork in #8