Exposing GLCanvas.setZOrderMediaOverlay as React Native prop. Setting
it to true put the new SurfaceView above the previous. Fixes issue #131

- format: "base64" || "file"
- type: "png" || "jpeg"/"jpg" || "webm" (android only)
- quality: from 0 to 1 (iOS support only with type=jpg/jpeg)
- filePath: for format=="file" you must provide a file path (you can use react-native-fs to get directory constants)