Env is not passed to card components

[palcisto]

I am trying to leverage this lib to render mobiledoc using shared card components for both the editor and end-user display, however our components are not being passed the env object per the Mobiledoc-kit Card.

Specifically, we're currently trying to leverage the env.isInEditor. However, we don't want to be limited to just that for future needs.

I would be glad to create a PR to introduce the necessary changes.

I hope that we can proceed with next steps within the next week or so, as our team is looking to utilize this addon very soon.

Cheers!