Fix cast time talent bonus of channeled spells

This fixes the cast time talent bonus of channeled spells, including Improved Succubus.

The only changes of file Unit.cpp is the new function:

```
void Unit::ModChanneledSpellCastTime(SpellInfo const* spellInfo, int32 & castTime, Spell* spell)
{
    if (!spellInfo || castTime < 0)
        return;

    // called from caster
    if (Player* modOwner = GetSpellModOwner())
        modOwner->ApplySpellMod(spellInfo->Id, SPELLMOD_CASTING_TIME, castTime, spell);
}
```

I don't know why diff shows delete+add of the same lines.