Add HEIF/HEIC mime types

[bgarel]

HEIF is the new image format that is now preferred and official in iOS 11 and macOS 10.13. Please add

• image/heif => heif
• image/heic => heic

https://www.iana.org/assignments/media-types/media-types.xhtml

[hey-red]

Thanks for link, I'm try to add it as additional source.
However, you can add this to your app like this:

MimeTypesMap.AddOrUpdate("image/heif", "heif");
MimeTypesMap.AddOrUpdate("image/heic", "heic");