S3ImageCropWidget v2.0

This widget includes the following enhancements or features:
* Improved UX.
* Cropping done completely at Client-Side. 
* Once cropping is done, you can see the Image cropped before even uploading.
* Fixed bugs or defects.

- This has been tested on modules like document, staff, volunteer and person registry in the default template.
Should we not .lower() in the check rather than including here?
We could make this a tuple too? (slightly better performance and this is currently executed every request...perhaps better even to move this to a module too?)