Adds a generic projectile hit sound to most projectiles, except for practice laser and laser tag beams. Scales volume of projectile hit sounds by damage done by the specific projectile.

Overrides the generic sound with specific ones for electrodes and
lasers: sear.ogg for lasers and "sparks" for electrodes.

Thanks @optimumtact for your help with getting the hitsound volume scaling to work.
Merge pull request #2481 from Tenebrosity/projectileimpactnoises

Adds generic impact noises to all projectiles