Updated the linker to handle the meta-model changes to
ContainedNamedElements and ContainmentPathElements.  Fixes #454.
Prevent NPE when calculating hash code
Changed handling of owned/referenced property type and units type -
fixes #411
When linking a chained ContainmentPathElement, get the previous element
by going up the containment hierarchy instead of getting the list of
ContainmentPathElements.
Fixed two RuntimeExceptions regarding ContainedNamedElements and
ContainmentPathElements that can occur when the model is invalid, such
as when in the midst of typing a model in the editor.
Fixed multiplicity typo in metamodel
Fixed outline label for numeric property types - fixes #408
Added comments to explain why dead grammar rules are left in the parser.