Serialization: sort entity types and subject/object definition to let it be deterministic
For now this serialisation is randomize, it means the order is not always the same. For example we can obtain :
class rel1(RelationDefinition):
subject = ('FirstClass', 'SecondClass',)
object = ('FirstClass', 'SecondClass',)
or
class rel1(RelationDefinition):
subject = ('SecondClass', 'FirstClass',)
object = ('SecondClass', 'FirstClass',)
Which could leads to error. Especially for the owl2yams
project tests