add REST documentation for mediacore module

The [Swagger specification](https://github.com/wordnik/swagger-spec/blob/master/versions/1.2.md) does indeed say:

> If paramType is "body", the name is used only for Swagger-UI and Swagger-Codegen. In this case, the name MUST be "body".

I had previously considered (actually, more than considered, I tried it out with a few endpoints) documenting these parameters as FORM parameters rather than BODY parameters. It sort of works, but seems really hacky and might cause problems in the future.