new flag for fields: show field content when empty

composer/schema/factory.py

@@ -105,6 +105,7 @@ def createField(field, info=None):
               readonly=field.readonly,
               #value_type=getattr(field, 'value_type', None),
               nostore=getattr(field, 'nostore', False),
+              showEmpty=getattr(field, 'showEmpty', False),
               multiple=getattr(field, 'multiple', False),
               display_format=getattr(field, 'displayFormat', None),
               baseField=field,)

composer/schema/field.py

@@ -49,6 +49,7 @@ class Field(Component):
     required = False
     readonly = False
     nostore = False
+    showEmpty = False
     standardFieldName = None
     vocabulary = None
     renderFactory = None