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

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

Maintaining an alias for the new EmComponent.db_engine

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

Passe tous les tests

Now _fields and table MUST be class attribute.
Its important to note that _fields now consist in a list of (name, ftype) tuples and that ftype is a EmFieldType class and NOT an EmFieldType instance

- Now except for the modify_rank tests test_component didn't fails
- Added simple integer operation capabilities to EmFieldType_integer ( int cast, +=, -=, *=, /=, +, -, *, /, %, ...)

EmComponent.create() now takes keywords arguments corresponding to the _fields property of the calling class

WARNING !!! Hardcoded rank = -1 at component creation and Hardcoded 0 as default value for EmClass icon

Correction du bloc de mcommentaire de class encore sous l'ancien modèle.

remplacement des self.id restant par self.uid

Now EmComponent is populate if it's instanciated with a name or an id

Pass the value of ranked_in instaed of the column name.

same as precedent

test si new_rank - 1 existe pour signe '='

En cas de signe égale prend désormais en charge une valeur de new_rank superieur ou inferieur a la valeur actuelle.

En plus de modifié la valeur en base, modifie la valeur d'instance.

Prise en compte du nom de la collonne indiqué par ranked_in

Fonction new_rank dans component. Permet la modification d'un rank tout en gardant la collection de component valide.

The dates are set in EmComponent::create() for date_create and in EmComponent::save() for date_update
The values are sets to datetime.datetime.utcnow() so we now that EVERY date in the db are in UTC, no matter django, database or even server configurations.
We will have to take care to convert dates from database to django timezone in dates fieldtypes.