Spawn Projectiles as Children of a GameObject

Right now, Projectile game objects clutter up the game hierarchy. Would be good to pass in a `parent` parameter to `Shooter.cs -> FireSingleShot` so the hierarchy is cleaner.

Open Shooter.cs and inspect the FireSingleShot entry point and how projectile GameObjects are created. Trace the firing call to determine where the parent should be supplied, then verify in Unity that fired projectiles appear under the requested parent in the game hierarchy.

Written by the indexing model from the issue text.