Added support for Apple's HEIC image format

Some Apple devices are configured to send the raw HEIC image files and that can cause issues. 

Thanks to one of our uses that reported problems uploading images, it was found that their iPhone was taking images in the raw HEIC/HEIF format and our system (and most websites) won't accept them.

After a little work, I was able to detect this image format and convert it to JPG format on the fly. The process is a little slower when uploading images but at least now you don't have to do the pre-processing yourself before trying to upload HEIC images.