Implementation changes

List of all `from_etree` methods

Class	Accepts etree	Standart format	Method signature	Note
Schema	Yes	Yes	def from_etree(schema_nodes, config: Config):
StructType	Yes	No	def from_etree(cls, type_node, config: Config):
EnumType	Yes	No	def from_etree(type_node, namespace, config: Config):
EntityType	Yes	No	def from_etree(cls, type_node, config: Config):	Should be
EntitySet	No	Yes	def from_etree(entity_set_node):
StructTypeProperty	No	Yes	def from_etree(entity_type_property_node):
NavigationTypeProperty	No	Yes	def from_etree(node):
EndRole	No	Yes	def from_etree(end_role_node):
ReferentialConstraint	Yes	Yes	def from_etree(referential_constraint_node, config: Config):
Association	Yes	Yes	def from_etree(association_node, config: Config):
AssociationSetEndRole	No	Yes	def from_etree(end_node):
AssociationSet	Yes	Yes	def from_etree(association_set_node, config: Config):
Annotation	Yes	No	def from_etree(target, annotation_node):
ExternalAnnotation	Yes	Yes	def from_etree(annotations_node):
ValueHelper	Yes	No	def from_etree(target, annotation_node):
ValueHelperParameter	Yes	Yes	def from_etree(value_help_parameter_node):
FunctionImport	Yes	Yes	def from_etree(function_import_node, config: Config):