public static ActivityBuilder activity() {
    return new ActivityBuilder(null);
  }
Create {@link ActivityBuilder} instance to open image picker for cropping and then start {@link
CropImageActivity} to crop the selected image.<br>
Result will be received in {@link Activity#onActivityResult(int, int, Intent)} and can be
retrieved using {@link #getActivityResult(Intent)}.

@return builder for Crop Image Activity
core/src/main/java/com/theartofdev/edmodo/cropper/CropImage.java