Extend the Introspection class to provide information about the base
elements of the composite finite element used everywhere.
Convert a number of places where we had hardcoded base element indices
by search/replace. A few places still need to be looked at.
Add a number of definitions for member variables, including one we
appear to have forgotten previously.
Some more conversions of explicit base element numbers.
Provide some more cleanups.
Some more generalizations now possible with the extended Introspection
class.