PLUS : Stopping a power plant costs money

* Stopping a power plant costs : the cost of the plant divided by 8.
BUG FIX : Projectiles not hitting enemies
BUG FIX : Fully destroying buildings

* I forgot when destroying a tower, to destroy the trigger area as well
PLUS : Tower range appears on tower select

* the material of the tower triggers changes to something more visible
when the tower is selected.