gl-react + react-native-view-shot : write a third lib that makes it easier

[@greweb]

to recreate this example https://projectseptemberinc.gitbooks.io/gl-react/content/docs/examples/8.html

basically it would be like

<Surface>
  <GLBlur>
    <RasterizeContent>
      <View>.......</View>
    </RasterizeContent>
  </GLBlur>
</Surface>

[@greweb]

technically it should be feasible for the RasterizeContent lib to add a texture loader into gl-react that support its instance and would snapshot the thing. also think I should fix gre/react-native-view-shot#48 first so it's a simple use of that Snapshotable.

(RasterizeContent make have whatever different name)

[@greweb]

if some content needs to continously refresh, there could be a prop to set that. basically means to call context.glParent.redraw() in a render loop

[@greweb]

created https://github.com/gre/react-native-webgl-view-shot but now need to think how things will interoperate