Add focal point to images

[PaulKiddle]

We do automatic image cropping in our frontend framework. Sometimes important features of these images are cut off because we don't know where the focal point of the image is.

It would be great to be able to specify an image's focal point that we can serve in our API to the frontend along with the image URL & alt text.

It could also be used as a default value when creating a new curation in the CMS UI.