Investigate potential security concerns for not ignore DTD definitions in labels

[jordanpadams]

From security scan:

PDS-000004	12/31/18	Determine if the findings about the parsing of user-controlled XML documents is valid, and determine the potential consequences if they are.	med	preparation/pds4-tools/src/main/java/gov/nasa/pds/objectAccess/ObjectAccess.java	163	Resolving XML external entity in user-controlled data (CWE-611)	Resolving XML external entity in user-controlled data (CWE-611).  Parsing user-controlled XML documents and allowing expansion of external entity references may lead to disclosure of confidential data or denial of service.	Y	More research needed, but this couldbe relevant.			CWE-611	The best way to prevent XML External Entity attacks is if possible disable the parsing of any Document Type Declarations (DTDs) in untrusted data. Many XML parsers for Java are a know and easy target for exploitation.