Add support for entity category in AttributeRelease policy management

[janul]

Right now you can manage attribute release policy based on requester (entityID) - it's good but it might be quite heavy to consume by Shib-idp if in there is few thousands serviceproviders in you circle of trust.
Implementing this new feature will be quite tricky:
*) to merge into current logic
*) keep backward compatibility
*) (not confusing) presentation and management
Any proposals are welcome

[janul]

update: new ARP generator currently in develop branch:
*) including entitycategories based rules
*) backward compatibility

• you can compare original arp with new one:
  • url for current arp: https://HOST/ALIAS/arp/format2/ENCODEDENTITY/arp.xml
  • experimental url: https://HOST/ALIAS/arp/format2exp/ENCODEDENTITY/arp.xml

*) PHPDom replaced by XmlWriter

*) performance increased by 60%

*) UI to manage arp rule based on EntityCategories is not ready yet