Add flag for rendering key value, for enum field renderers

Only valid during the readonly rendering.  Not sure how useful this will
be in the long run...

tailbone/forms/renderers/common.py

@@ -158,12 +158,13 @@ class EnumFieldRenderer(SelectFieldRenderer):
     """
     Renderer for simple enumeration fields.
     """
-
     enumeration = {}
+    render_key = False
 
-    def __init__(self, arg):
+    def __init__(self, arg, render_key=False):
         if isinstance(arg, dict):
             self.enumeration = arg
+            self.render_key = render_key
         else:
             self(arg)
 
@@ -174,8 +175,11 @@ class EnumFieldRenderer(SelectFieldRenderer):
     def render_readonly(self, **kwargs):
         value = self.raw_value
         if value is None:
-            return u''
-        return self.enumeration.get(value, unicode(value))
+            return ''
+        rendered = self.enumeration.get(value, unicode(value))
+        if self.render_key:
+            rendered = '{} - {}'.format(value, rendered)
+        return rendered
 
     def render(self, **kwargs):
         opts = [(self.enumeration[x], x) for x in self.enumeration]