Some fixes to Mark's fix. Removed Deer's age

A decision was made to follow the client’s request (or lack of it) and
not implement an aging mechanism to deer.

A bug was when deer did not move out of their current point. The
iterator’s remove command would remove them anyway and a significant
loss of deer was apparent. That was fixed by returning a boolean value
from Mover. If the deer indeed stayed in the same location, Mover will
return false and therefore the organism will not be removed from the
grid.