Moved combatant creation logic to new file

In other words, there is now a combatant entity file.
Added TODO note in Physics.lua
Added "dumb" deployable turret
Fixed minigun not spinning down on overheat
Made miniturret default search radius reasonable
Modified ArenaBounded, added DestroyOutsideArena

ArenaBounded now must be on an entity for it to bounce off arena walls.
Added projectile spread to projectile weapons
Tweaked and added minigun defaults
Explosion now only affects CollisionPhysics
Made shotgun recoil consistent with rest of weapons
util.table.clone is now a deep clone

ie. It clones all tables in the table and all tables in those tables,
etc.
Updated test.lua
Added OnSpawn and OnDestroy components

These are called by the world.
Fixed minigun not deleting effect entity
Gave miniturrets default health
Added rotation smoothing
Removed unused function
Updated TODO