Implementation of ServiceFactory
Fixing the name of the methods for obtaining instances in ServiceFactory
Test cases: 'unknownClass', 'nullClass' and 'classWithKnownAttributesAndWithoutConfiguration' for Instance. Adding the validation AttributeValue in InstanceHelper
fixing the assertion default name for instance tests
Assigning a default value if available, an AttributeValue case is null
Fixing the refactorings needed for merge # 50
fixing the assertion default name for instance tests
Implementation of tests involving instances and configuration of attributes