Associated tests has been added/updated

Now on load default fields for EmClass are created. The EmClass.check method create them if they are not present.

Added default fields for EmClass, they are listed by classtype in EmClassType
Fixing some tests (testing that a new EmClass has no fieldgroups)
Fixing the delete_check of EmClass. Now an EmClass can be deleted if it contains only default fieldgroup and default fields

No extended checks was done. Only tested if the check passes without syntax error and without failing with no reason

EmComponent::check() always return True but rearrange ranks if they are not continuous

There is now two methods Model.name_from_emclass and emclass_from_name that allows to access the Model.components array

- Suppression des méthodes SQL

Cette vérification est prise en charge dans EmComponent

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

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)...

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

ignoring:
 - line too long
 - doctring

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