Artifact balances/bugfixes

Changelog:

* Improved orb of light tracking and movement, increased layer and
decreased alpha
* Extinguishing artifact now extinguishes humans
* Extinguishing artifact now cools down humans
* Fixed some update_icons issues
* Fixed on-click saplife ability
* Fixed wormhole runtime errors caused by trying to pick tiles from an
empty list
* Decreased shadow mob lifespan
* Decreased shadow mob visibility
* Shadow mobs now cause hallucinations instead of brain damage
* Nightmare ability no longer causes brain damage
* Added a message when detection/location ability doesn't detect any
nearby artifacts
* Added small cooldown for detection/location ability
* Added on-click pull/push ability cooldown
* A message now appears when healed by healing ability
* The melee ability now exclusively activates upon melee attack
* Melee ability now displays an attack message on hit
* The dirt ability now has a chance to create xenoblood
* Fixed forcewall length
* Decreased forcewall ability cooldown
* Fixed some abilities not working with ranged artifacts