[s2717] Implement Onyxia spell Heated Ground

Note: Adapt your mangosd.conf to have a larger value for "MaxSpellCastsInChain" (12 is required, better be safe than sorry and use a big value :-) )

(based on commit 87adee2)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>