core (memory): entities cache improvments:

- entities cache is no more limited to bare jid
    - resources are now automatically updated in bare jid cache

src/core/constants.py

@@ -40,6 +40,7 @@ class Const(object):
     PROF_KEY_NONE = '@NONE@'
     PROF_KEY_DEFAULT = '@DEFAULT@'
     ENTITY_ALL = '@ALL@'
+    ENTITY_LAST_RESOURCE = 'last_resource'
 
 
     ## Configuration ##