[cleanup] Updated document to the new xar format.

(cherry picked from commit 0fc6d1e1bba7fbb936106e4dab879a8488e9748a)
XWIKI-11556: Some skin resources are requested with absolute paths instead of relative ones

(cherry picked from commit 4ae6023d6304203f5d4175ff611e9b1f8859c474)