Multiple issue fix for crop function

[LeGoffMael]

• export CoverStyle

• Crop bug fixes:

  • fix crop prefered aspect ratio on landscape video
  • init CropScreen with prefered aspect ratio Preffered Aspect Ratio on crop not working properly. #17

_controller.initialize().then((_) {
  _controller.preferredCropAspectRatio = 1;
  _controller.updateCrop();
  setState(() {});
});

• rotation is synch with controller on CropScreen
• crop in init of CropScreen without gesture cannot crop #16 (maybe?)