Add possibility to customizing file name

Hi developers! It will be great to add somehow possibility to change file name. It is no critical, but it will be helpful in future.

I had situation when I has needed to change file name, so I made replacing file name before sending to the server. It is ok, but it will be grate to setup file name (or at least prefix) in the builder of CropImage.

https://github.com/ArthurHub/Android-Image-Cropper/blob/2a4a425668bfff1329dd5bfb1b80b0829bb4cc67/cropper/src/main/java/com/theartofdev/edmodo/cropper/CropImageActivity.java#L294

Thanks!