Decoupled Instagram Engine of Instagram media

I have decoupled actions in `InstragramEngine` class of model `InstagramMedia` because I already have a model to use it with CoreData and I consider that is not necessary to use all the model when you only need the ID parameter. 

This way you can use any model working with Instagram media and you don't need to store references, or create `InstragramMedia` objects to do any action.

What do you think?