[z1844] update creature's unit part(update spell events, auras, movement) while in death. thanks to rsa for making tests

this allows us update creature's death persistent auras, fall died creatures in natural, non hacky way

also fix the bug that creature starts waypoint movement not from begining at respawning. thanks to Grz3s for reporting

(based on commit 3d73fd6)

(cleaned version of 1cae4ec)

(based on commit [s1405] - 9ebaee8)