Schema and SgFieldSelectionList updates

Schemas no longer save out empty field data, in particular,
valid values, value types,summary info,  data.

SgFieldSchemaInfo added displayValues() function.  Used by selection
list fields, see SgFieldSelectionList commit info.

SgFieldSelectionList added displayValue() for returning the display value.

Status fields store there value as a short name, you can use displayValue()
for returning the user friendly long name.