Fixes BearTrap message, sound and other things

* Fixes #3496 (icon update)
* Space carps and bats can no longer step on beartraps
* Adds sound for the snapping beartrap
* Aliens and Monkeys can now trigger beartraps.
* Gives beartrap attack message in all cases.
* Beartrap now deals damage to all of its victims, including humans.
* Adds stun effect for non human victims.