Add missing fields to ApodContent

[Giorgi]

Is your feature request related to a problem? Please describe.
The ApodContent does not expose all data returned in the json response

Describe the feature you'd like
Add all data (such as concepts, thumbnail_url, etx) to the ApodContent class

[MarcusOtter]

Thanks for this, the API has most likely been updated a lot since the last release. Will see when I have time to look into it.