Modified LeObject adding a _datasource_name attribute

The _datasource_name attribute replace the old _datasource attribute. The goal of the modification is to maintain easyly accessible datasource UID

lodel/leapi/lefactory.py

     _abstract = {abstract}
     _fields = None
     _uid = {uid_list}
-    _datasource = {datasource_name}
+    _datasource = None
+    _datasource_name = {datasource_name}
 
 """.format(
     clsname = LeObject.name2objname(em_class.uid),

lodel/leapi/leobject.py

     @classmethod
     def _init_datasource(cls):
         expt_msg = "In LeAPI class '%s' " % cls.__name__
-        datasource_orig_name = cls._datasource
-        if cls._datasource not in Settings.datasources._fields:
+        datasource_orig_name = cls._datasource_name
+        if cls._datasource_name not in Settings.datasources._fields:
             expt_msg += "Unknow or unconfigured datasource %s"
-            expt_msg %= (cls._datasource, cls.__name__)
+            expt_msg %= (cls._datasource_name, cls.__name__)
             raise SettingsError(expt_msg)
         
-        ds_identifier = getattr(Settings.datasources, cls._datasource)
+        ds_identifier = getattr(Settings.datasources, cls._datasource_name)
         try:
             ds_identifier = getattr(ds_identifier, 'identifier')
         except NameError:
             expt_msg += "Datasource %s is missconfigured, missing identifier."
-            expt_msg %= cls._datasource
+            expt_msg %= cls._datasource_name
             raise SettingsError(expt_msg)
 
         ds_plugin, ds_name = ds_identifier.split('.')