Percentage props support

Now we can use percentage props on shape elements:
Rect,Circle,Line, Ellipse

<Rect x="0%" y="5%" width="90" height="95%" />
<Circle cx="50%" cy="50%" r="50%" />
<Line x1="0%" y1="5%" x2="90%" y2="95%" />
<Ellipse cx="50%" cy="50%" rx="30%" ry="40%" />

And moved gradients percentage calculation to native side for a better support.

First release

• Change npm package name from react-native-art-svg to react-native-svg.
• Isolated from ReactNativeART.
• Add some SVG features support (ClipPath, strokeOffset, gradients stroke).
• Fix some issues on ART.