ISPN-4528 Genericize remaining M/R internal classes

Master only. See https://issues.jboss.org/browse/ISPN-4528 for more details. 
I wouldn't be adverse to just having a separate commit in this PR pointing to the new JIRA that changes that.

And actually looking into MarshalledValue a bit closer, it appears that EntryIterator is broken when marshalled values are used.