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

Added class graph, caller and call graph

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

Conflicts:
	EditorialModel/components.py

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

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)