Parsing invalid model/instance XMI

[cfi-aschneider]

Two cases of parsing invalid models/instance XMI were not being caught:

1. An invalid eSuperType in a ecore model file is parsed and discarded silently.
2. An invalid xsi:type of a child in an instance is also parsed and discarded silently.

Initial error throws have been added to our repo in the resolve references and parse routines that detect the undefined items which cause silent discarding. Related tests have also been added.