[CMS-2951] Universal XSLT helper - JIRA Ametys

to bring them all and in the darkness bind them

Progress

1.	Add a helper to give access to the whole sitemap as a DOM	Closed	Unassigned
2.	[XSL Variables] $site, $skin are not available in all XSL of services	Closed	Cédric Damioli
3.	Add a helper to test the existence of resources in my skin or in the resource explorer	Closed	Cédric Damioli
4.	Add a helper to list resources in my skin or in the resource explorer	Closed	Unassigned
5.	Add a helper to test the existence of i18nkey in my skin	Closed	Unassigned
6.	is a page with limited access	Closed	Cédric Damioli
7.	Get the category of a tag from its id	Closed	Cédric Damioli