- 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

- Now returning automatic common field classname in fields method

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

- now datasources are declared with two conf keys : read_only and identifier
- the old datasources plugin hook is now declared in lodel/plugin/core_hooks.py. This file is imported after lodel/plugin/hooks.py in the loader.py

- Enables connections saving & auto cleaning
- Preparing possibility to declare a datasource as read only

- Now delete & update methods use filters & rel_filters

- deleting most of **datas to replace it with a standart dict argument
- using filters in childs of LeFilteredQuery