ESDEV-2372 Send all serial keys when new one was added ESDEV-2390 Send existing keys and new key as new tag

Refactoring oxSimpleXml class.
ESDEV-2372 Send all serial keys when new one was added ESDEV-2390 Send existing keys and new key as new tag

Adding possibility to add attributes with oxSimpleXml.
ESDEV-2372 Send all serial keys when new one was added ESDEV-2390 Send existing keys and new key as new tag

Renaming method.
ESDEV-2372 Send all serial keys when new one was added ESDEV-2390 Send existing keys and new key as new tag

Adding comments.