Methods are written.
They are not called by anyone and the only tests that were done is that no syntax error is raised.
( refs #131 )

- DatasourcePlugin implmentation as child class of lodel.plugin.plugins.Plugin
- moved methods about datasource initialisation from LeObject to DatasourcePlugin ( _init_datasource(), plugin_name(), _get_ds_connection_conf() ...)

Deleted hardcoded condition that brokes standart field validation process

- Add an update feature to create_instance.sh script
- Updated webui plugin load instruction (running loader.start() in run)
- Updated the way EmCmponents handles EmGroup
- Updated the way EmFields handles EmClass
- Updated xmlfile translator according to EmComponent modification

Now lefactory populate a LeObject attribute named _child_classes

	The UniqID datahandler has to call the datasource
	LeObject has to be able to determine wich parent class define its UID datahandler
	[NOT IMPLEMENTED] the datasource should be able to select with an abstract LeObject as target ( see #92 )

- Replaced a self. by cls. in leobject
- Changed default value for runtest option

- Changed the way of instanciating results object in get (using __new__ )

- 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