Core/Spells: drop last leftovers of hardcoded spell target selection and move it into spellscripts

Closes #1719
Closes #3186
Core/Misc: Missing changes and get rid of useless method in acd46085d1f496657e27e0d5f823f53d466702dc
Core/Splines: Fix "velocity > 0.1f" error

Updates #6191.
Scripts/HoR: Fix log error

Fix "DoZoneInCombat called for creature that has empty threat list" error caused by DoZoneInCombat() called by IsSummonedBy() in a script before the Creature is allowed to enter combat.
Fix warnings introduced on littleendian in 2134cb610d45727a0623741f7416a360882133fa

This fix prevents possible issues on bigendian machines. Don't use c style casts ppl, it's evul.
Core&DB/Spells: Move custom spell attributes from code to DB, `spell_custom_attr` table

`spell_custom_attr`
- `entry` uint PK
- `attributes` uint (enum SpellCustomAttributes of SpellInfo.h)
SQL: Update old .sql files to keep consistency with auth_database.sql

Also update characters_database.sql (generated by mysqldump)
Core/Spells: Fix DK Ghoul's damage after ad8eb434c02e451effd0949aaa7d2b7999d91597. I misread 'SpellScript::m_damage' for 'SpellScript::damage'.

By @joschiwald
SQL: Fixed two issues with 2014_01_31_00_world_spell_custom_attr.sql

Engine should be MyISAM and not MRG_MyISAM
MySQL doesn't play nice with hex values so converted them to decimal

Closes #11537
Core/Achievs: Rename a few unknown achievement criteria flags

Source tomrus88, Mangos
DB/item_template: Set defaults of spellcharges_X to 0 instead of NULL

Closes #10748

Signed-off-by: Duarte Duarte <dnpd.dd@gmail.com>
SQL: Update 2014_01_31_01_world_item_template.sql
Core/Arena: Fix arena season not always appearing to clients

Arena season sent to client with SMSG_INIT_WORLD_STATES opcode was not sent if Player was on a zone with id 0 on login. Initializing the zone id to -1 will always trigger UpdateZone() properly on login.
Fixes #10623