[s2691] Improve script of npc_kelerun_bloodmourn

(based on commit 725d0c2)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>
Improve Nazan and Vazruden script (first part)

(based on commit 9e71cb1)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>
[s2691] Improve Nazan and Vazruden script (second part)

Change:
* Add support for nazan to dismount if his health drops below 20%
* Fix Nazan not attacking while he is supposed to fly (previous commit)
* Fix some possible FAIL glitches (previous commit)

(based on commit 1ad331c)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>