Adds a three-second cooldown to the alien hunter pounce

Does as the name implies. I was inspired to make this after a round on Sybil in which one alien hunter knocked down an entire deathsquad. Pounce is still viable, but far less spammy.

In addition, you are put out of leap mode if you land a leap successfully. If you hit nothing or slam against an object, you stay in leap mode.
This should probably be leap_on_click = 0 and leap_icon.icon_state = "leap_off", otherwise if the player toggle leap off mid-leap then the successful knockdown would turn it back on.