add REST documentation for mediacore module

When looking at a few other Swagger examples, I came across an example that has both the body approach (e.g. http://petstore.swagger.wordnik.com/#!/pet/addPet) and the form param approach (e.g. http://petstore.swagger.wordnik.com/#!/pet/updatePetWithForm).

The body approach seems to be used when a full object (real model) needs to be sent through, whilst the form param approach is used when a number of specific fields need to be provided. That separation makes sense to me, and would mean that we should use a form parameter in this particular case.

@sathomas : What do you think? /cc @simong @mrvisser @stuartf