[8775] implement all creature difficulties + support bgs with this

former know as heroic_entry we now have 3 of those
which let us chose different creature_templates for different
map-types

normal maps will need a bit more support to use correct
spawnmodes

but for battlegrounds it works already good:
they are divided by levelrange:
    0-59  == normal spawn -> spiritguides level 60
    60-69 == difficulty=1 -> spritiguides level 70
    70-79 == difficulty=2 -> spiritguides level 80
    80    == difficulty=3 -> spiritguides level 80

this is needed mostly for alterac valley to get
right creature-templates spawned
and with that all creature->SetLevel hacks could
get removed from alterac valley code

sql/updates/8775_02_mangos_creature.sql

@@ -0,0 +1,10 @@
+ALTER TABLE db_version CHANGE COLUMN required_8775_01_mangos_creature_template required_8775_02_mangos_creature bit;
+
+-- cause bgs now have different spawnmodes all creatures on those maps must go
+-- to all spwanmodes.. maybe this isn't valid for all creatures - but i won't
+-- destroy again all bgs :p
+-- 0x1 = 2^0 - normal
+-- 0x2 = 2^1 - difficulty_1
+-- 0x4 = 2^2 - difficulty_2
+-- 0x8 = 2^3 - difficulty_3
+UPDATE creature SET spawnMask = (0x1 | 0x2 | 0x4 | 0x8) WHERE map IN (30, 489, 529, 566);