Add support for Core Data model

Instead of just copying the `xcdatamodeld` file, it has to be compiled first - like xib and storyboard files.

I've seen a [workaround](https://gist.github.com/alloy/38a3400bffc0837af5f3) to add Core Data model files as a resource, where the `xcdatamodeld` file is compiled first and the resulted `momd` files is added as a resource. I don't like this solutions because it adds overhead to the `podspec` file and I have to do it for every model file.

I'm not sure why this hasn't been implemented already in the install resources script - seems so obvious...