DB/Misc: Traveler's Tundra Mammoth from Dr-j

Script vendors on Traveler's Tundra Mammoth so that when player
dismounts they say there line before despawning

Scripts: -
* Hakmud of Argus <Traveling Trader>  - http://www.wowhead.com/npc=32638
* Gnimo <Adventurous Tinker> - http://www.wowhead.com/npc=32638
* Drix Blackwrench <The Fixer> - http://www.wowhead.com/npc=32641
* Mojodishu <Traveling Trader>- http://www.wowhead.com/npc=32642

Only the first texts by each of the horde vendors is from sniff, rest
taken from wowhead

Closes #11349