Cette vérification est prise en charge dans EmComponent

Changed beahvior : when a 'non-change' is asked (like +0 -0 or set ranke to actual rank) don't raise an Error

Implemented __hash__ and __eq__ for EmComponent (based on class name and uid) to test equality betwenn two instance. Allows to use "instance in instance_list" syntax

Behaviour changed for EmComponent and childs create method :
	- Takes care of duplicated names at creation
	- Handle all the checks in EmComponent method
Factorization of EmField.get_class_table() method
Added a @property method class_table_name to EmClass

Added docstrings comments to tests (for fancy output with -v ).
Fixed strange hidden failure that make tests stops on non failed tests with -f option. Those false failure seems to comes from with self.subTest blocs with functions calls that does assertion.

Moved the database initialisation functionnality to sqlsetup and fixed all the code to handle the sqlwrapper deletion

Every tests passes, except the skipped tests on relation_to_type links
There is a strange warning that comes maby from some tests (but maybe not)...

Added hierarchy tests

Maintaining an alias for the new EmComponent.db_engine

Actually not able to check relation_to_type deletion constraints

The EmField version cannot be tested yet (drop column not yet implemented for sqlite in Database.sqlalter)

Also add a new function is sqlutils to execute ddl

 + pep8 and pylint

ignoring:
 - line too long
 - doctring