Not tested because of bugs in EmField

Changed comments about EmFieldGroup.fields()

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

Passe tous les tests

Récupération dans EmComponent directement

Suppression du init et passage des classes plutôt que les instances pour les fieldtypes dans le _fields

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

Cleaning code for EmComponent
Optimizing tests for EmComponent and EmFieldGroup (running initDb in setUpModule and make a backup copy, the backup is restored in setUp)

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

Maybe very bugy

Written some test setup and the begining of the __init__ test

- Added a _fields property (also added it as class property, but the way its done is not satisfactory... we want an ordered dict and not a tuple list as class property)
- Its now allowed to give an uid or a name as em_class for EmFieldGroup.create(name, em_class).
- Now when EmFieldGroup.create is called with an existing name it raises an error (ValueError)
- Removed EmFieldGroup.populate and EmFieldGroup.save

Now an MlString instance is able to say if another MlString instance is equivalent using mlstr1 == mlstr2