[3076] Complete setup for the first encounter in ToC5

This implements the following:
* transition between first arena challenge (with mounts) and second challenge (normal combat)
* mount change for the champions
* grand champions encounter completion - this allows players to move to the second encounter (To be implemented)
* basic spells for first arena challenge (not completed yet)

Note: complete combat support not yet implemented
[3077] Make use of the new OnCreatureDespawn feature in ToC5

This allows vehicle mounts to respawn on passenger eject

Requires Cmangos 12803+