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

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

Also add a new function is sqlutils to execute ddl

EmType hierarchy is handled by 3 functions :
	- EmType.superiors()
	- EmType.subordinates()
	- EmType.add_superior(em_type, nature)
	- EmType.del_superior(em_type, nature)
Hierarchy implementation is not tested (because their is no tests...)

Added a function to get authorized relation nature from an EmClassType
Added the nature of a relation to the primary key of em_type_hierarchy table (triple pk : sup_id, sub_id, nature)

It takes an EmComponent child class as parameter and return an sqlalchemy Table

Using sqlite db in test_components

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.

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.

Added a classmethod EmComponent::newUid() that determines the caller's class and return a newly registrated UID

Put every uid columns and associated FK in INTEGER instead of VARCHAR(50)

Adding a column is implemented for mysql, postgresql and sqlite.
Droping and altering a column is only implemented for mysql and postgresql for the moment.

Quick&dirty tests has been done  for sqlite and mysql only.

To-Do: tester

To-do: prendre en charge le cas de execute ou une query a des parametre binder et une liste de dictionnaire est envoyé en param

Implementation d'alias au ordre sqlalchemy: select, select_from, where, update, execute
To-Do: implemente insert et delete, tester.

Now SQLSetup in able (via initDb) to initialize the database.
WARNING : initDb start by droping all tables in database before creating the new ones