Fix Spectral Arrow hack code

[kphoenix137]

Based on: #6336

Refactors logic regarding "Spectral Arrow"

In AddSpectralArrow(), this function is set up as if it was a function for an actual arrow; setting up missile velocity. The velocity is altered by player class and items that increase attack speed. The velocity is passed in var3 which was used in ProcessSpectralArrow as spllvl, which affects the velocity of Fireballs shot from Flambeau, (and perhaps Blitzen and Thunderclap, but was not tested). The velocity is increased by using a Rogue, Warrior, or Bard, as well has having items that increase Attack Speed (which is impossible when wielding a bow), which is the reason I believe this was done in error.

The missileID is no longer extrapolated from player lightning damage (considering this has proven to cause bugs), but instead now iterates equipment items and check if the iterated item is Unique, and checks the item powers it has to find out if it has one of the applicable effects, and writes it to the missile struct as var4.

I considering adding Hellfire Item Effect flags for these items, however I think that would cause reverse compatibility problems.

[AJenbo]

Needs a rebase