Scripts/HallsOfStone: Sjonnir, some improvements

- rewritten to BossAI
- added spawn ordered by percent, according to official data

Closes #10702

Signed-off-by: joschiwald <joschiwald@online.de>

sql/updates/world/2013_09_02_19_world_spelldifficulty_dbc.sql

@@ -0,0 +1,7 @@
+DELETE FROM `spelldifficulty_dbc` WHERE `id` IN (51849, 50840, 50834, 50830, 50831);
+INSERT INTO `spelldifficulty_dbc`(`id`,`spellid0`,`spellid1`) VALUES
+(51849, 51849, 59861),
+(50840, 50840, 59848),
+(50834, 50834, 59846),
+(50830, 50830, 59844),
+(50831, 50831, 59845);