Add content aware image cropping

[wvffle]

Describe the feature

At first I'd just like to say that you guys did a very good job with the project! :)

I'm lacking one feature from ipx that prevents me from moving to it completely and that is content aware image cropping. While doing research on the topic, I've stumbled upon https://github.com/jwagner/smartcrop-sharp. It's a working library that provides just that. Maybe it's a good starting point?

Additional information

• Would you be willing to help implement this feature?