Implement grenades and explosion effects

[modawan]

Grenades are considered to be "spells", so this includes all the work needed to add spells to combat mechanics.
For grenades we also need explosion effects and "sphere" object lookup routines.

Scripts for the cinematic fight between Sith and Republic soldiers on Endar Spire have grenade throw actions and scripted explosion effects.

[modawan]

Grenade action does not work in the cinematic on Endar Spire.