https://matrice.dev.theresis.org/authzforce/authzforce-core-authzforce
into develop

Conflicts:
	src/main/java/com/sun/xacml/PDP.java
	
Other changes:
Merge branch 'develop' of
https://matrice.dev.theresis.org/authzforce/authzforce-core-authzforce
into develop

Conflicts:
	src/main/java/com/sun/xacml/PDP.java

- Fix AUTHZFORCE-18, AUTHZFORCE-19; in particular,
constructor/getInstance method has been added to use JAXB for parsing
XACML elements instead of the DOM API
- Improved PolicyReference to handle PolicyIdReference as well as
PolicySetIdReference without code specific to Policy/PolicySet
(polymorphism with IPolicy, same way AbstractPolicy was used in original
Sunxacml for PolicyReference), PolicySetReference now useless
- Refactoring/simplification using IPolicy interface implemented by
AbstractPolicySet, xacmlv3.Policy, PolicyReference (meant to replace use
of AbstractPolicy in original sunxacml version, but this abstract class
cannot be used for that because Policy* classes already inherit an
abstract JAXB class)
- Refactoring of xacmlv3.Expression* classes: getInstance() in
Expression, and getInstance() in ExpressionTools -> all getInstance() in
ExpressionTools