add REST documentation for mediacore module

> Am I right in assuming this indicates that the full request body must be the serialized `MediacoreId` model object with `Content-Type: application/json` ?

That's right.

It would be nicer if the Swagger UI actually took advantage of the model definition instead of providing only a `textarea` (though, as noted earlier, there is a trick to get it to pre-fill the `textarea` with a stubbed model).