Simplify callback interfaces - name indirection

[tclune]

Originally, ESMF did not provide a mechanism to create a NamedAlias of fields. This necessitates a tedious lookup for each item in a callback state in which you use the callback standard interface name to "lookup" the name of the field that is actually used.

This change will mostly simplify on the import side. The export side also get simpler, but does involve one new step to create the named alias before adding to the export State.

@pcolarco - you may want to keep an eye on this one when it comes in.

[tclune]

Forgot to mention that we want this change in the develop branch as it will considerably simplify updating to MAPL3.