[2896] Implement script for Ahune - The Frost Lord

This boss is only active during the Midsummer event

Please note that some visual spells and proc auras, specific to the submerged phase are not yet implemented. They require additional research and core support.
Add some minor improvements to Zul'jin

This fixes some of the issues posted on #61
[2897] Add script support for quest 10540

Thanks to grz3s for providing the necessary data