Addon.xml -> skin version 2.5.6 (Frodo)

Version number needed to change, because of Frodo beta testers.
No backwards compatibility with XBMC Eden.
Revert "modified Listitem Thumb and fanart calls to new standard"

This reverts commit 6002c122da0e62846fb848f3bbb848fb8243b170.
Merge branch 'Frodo' of https://github.com/kibje/skin.neon into Frodo
Merge branch 'Frodo' into Frodo_randomitems