fix/stuck-wildlife: try not to poof wildlife that is currently onscreen

[myk002]

maybe require that onscreen wildlife is stuck for a longer time before resorting to poofing to reduce the "huh?" factor for observing players.

[realSquidCoder]

Odd idea, but stonesense can follow the df window and show only what's on screen. Perhaps there is code in there to know what's visible to the player and thus what we shouldn't poof? Also, we should probably remember things that were on screen recently so that they also dont poof if we look away for a moment.

[myk002]

Figuring what is onscreen isn't that hard of a problem -- the suspendmanager overlay is a good example of that, but yes a cooldown timer for visibility might be a good idea