Add progression stages for Winter Veil's Winter Hats to drop from dungeon bosses.

[heyitsbench]

Sourced from Wowhead, used existing Northrend dungeon boss loot as reference. Accounts for both vanilla content and TBC.

Here is the expected loot with this PR:

Red:
 -  Vanilla
        Cannon Master Willey - Strat
        Dagran Thaurissan - BRD
        War Master Voone - BRS
 -  TBC
        Botanist Freywinn - Bot
        Nethermancer Sepethrea - Mech
        Captain Skarloc - Durnholde
 -  WotLK
        Jedoga Shadowseeker - AK
        Grand Magus Telestra - Nexus

Green:
 -  Vanilla
        Goraluk Anvilcrack - BRS
        Darkmaster Gandling - Scholo
        Prince Tortheldrin - DM
 -  TBC
        Grandmaster Vorpil - Slab
        Grand Warlock Nethekurse - Shattered Halls
        Exarch Maladaar - Crypts
 -  WotLK
        Mage-Lord Urom - Oculus

[TheJesterrr]

A great report! Not only was it designed to have the hat drop in non-wotlk dungeons, it also encourages more folks to run dungeons! A true win-win!