- now we have a LodelHook to trigger migration handlers loading
- datasources initialization in dyncode is now trigger by a hook (lodel2_plugin_loaded)
- datasources loading by dyncode is better

- The LeUpdateQuery implementation is broken or at least have huge performance issue
- Moved LeObject exceptions and LeQuery exceptions in lodel.leapi.exceptions

Adding a field to all non abstract classes to store in DB the name of corresponding LeObject subclass

- Modified again the em_test to fit with testing purpose
- First test on multi datasource query written
- debugging of query.py

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

- renamed Plugins class to Plugin
- an instance represent a loaded plugin
- classmethod allows to preload & load plugins

- now _datasource attr contains an instance of the datasource, instanciated with options given in conf file

+ better log message for datasource bootstrap

- now datasources are handled in LeObject child classes
- plugins module now have a method to retrieve a plugin module

Now a backreference is represented by a tuple(LeObject child class, fieldname)

This implementation is broken because of relation data_handler. Backreference is a broken concept and relation data_handler too.