[4.3.4] Spells/Mage: Ring of Frost

Ring of Frost (http://old.wowhead.com/spell=82676)

A little bit of explanations about how this scripts work.

Fist of all we have spell `SPELL_MAGE_RING_OF_FROST_FREEZE` (http://old.wowhead.com/spell=82676) wich freezes enemies at a given position. On the script for this spell we're only filtering targets acording to the "ring" structure.

Secondly we have the spell itself, the `SPELL_MAGE_RING_OF_FROST_SUMMON` (http://old.wowhead.com/spell=82676). This one have two effects: summon the RoF npc and a periodic effect. We're using the periodic efect for making the mage cast the previous spell (`SPELL_MAGE_RING_OF_FROST_FREEZE`) at the summoned npc position on every tick.

Finally `SPELL_MAGE_RING_OF_FROST_DUMMY` is an aura wich lasts 3 seconds and is used as coalesce marker for the ring.

Anyway, this spell still need work on the npc; making it untargeteable, to not follow the mage and stay passive to enemies, wich I'm not sure how to do it properly.