Always create the "groups" set for new elements.

This allows a smaller initial knowledge base.

naive-nlu/tree_nlu/tests/gac_100.py

@@ -648,33 +648,21 @@ base_knowledge = {
     'icecream': {
         "groups": {'noun', 'object', 'comestible', 'sweet'},
     },
-    'cold': {
-        "groups": {'property', 'temperature'},
-    },
     'hot': {
         "groups": {'property', 'temperature'},
     },
     'summer': {
         "groups": {'epoch'},
     },
-    'earth': {
-        "groups": {'noun', 'object', 'planet'},
-    },
     'planet': {
         "groups": {'noun', 'group'},
     },
-    'color': {
-        "groups": {'property', 'group'},
-    },
     'green': {
         "groups": {'noun', 'color', 'concept'},
     },
     'fly': {
         "groups": {'verb'},
     },
-    'chile': {
-        "groups": {'noun'},
-    },
 }
 
 def main():