Convert membranes from send/recv to wrap interface
Having membranes serve not only as wrapping/unwrapping objects, but also as message passing objects complicates the model needlessly. We should instead have membranes implement a generic
wrap interface (which works differently depending on if they are internal or external membranes) that performs the wrapping procedure on objects.
To get the same effect as membrane send/recv, we just need to wrap an RP and have it behave normally.