Replaces BeamRadius with BeamWidth.

Allows for more fine-grained control over laserbeam width.
Changes name of LaserZap Explosion trait to HitAnim.

Additionally sets default HitAnim to null instead of "laserfire", to avoid crashes when neither a custom HitAnim nor laserfire anim are present.
Merge pull request #3339 from reaperrr/laserzap

LaserZap improvements rev.2