- 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

- 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

- Implementation of the delete, insert and insert_multi methods + first implementation of the select method in the MongoDB datasource
- Added parsing methods in the mongodb/utils module

- The check method checks, for now, if all the needed parameters are passed to the connection string
- A test class has been written with some bad connection args examples