Check that an EmClass.EmField exsists in dyncode

- webui now calls a hook to indicate a session end
- loader.py now set a lodel.dyncode module exposing dynmically generated code

- calling check_data_value on filters value to ensure value casting

- 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 )

- datahandler base class was not supporting default values due to a bug
- implements the datetime datahandler construct_data method

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

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