Kostia

Fix XXE vulnerability

2

## Fixes https://github.com/jpos/jPOS/issues/462

XXE vulnerability in GenericPackager

3

GenericPackager (as well as GenericValidatingPackager) are vulnerable to [XML External Entity (XEE) attack](https://owasp.org/www-community/vulnerabilities/XML_External_Entity_(XXE)_Processing). Here is the test example that reproduces it ```java @Test public void testXXEAttach() { try { String...