Core/Spells: some SpellInfo corrections

- Stormstrike (should stack on same mob for different enha shammy)
- Mind Melt crit increase should apply also to Mind Flay
- Sindragosa Icy Grip range (should be 30 yards not infinite)
- Ignis - Grab (should grab ignoring any invulnerability)
- Brundir - Lightining Whirl (should be interruptible)
iirc the real problem here is that Brundir should be interruptable.
if you look towards the cant do that while stunned achievement his chain lightning must also be interruptable.
you should fix this by removing the flag from mechanic immunities in creature_template