Animated movement now controlled by speed

Instead of passing duration the speed is used to calculate the duration.
Commented out image_url from birds and nests

Sprite animation better and it is just clutter. But commented out until
certain and then removed.
Fixed bugs just introduced

Two places where speed wasn't introduced correctly and one where
image_url wasn't removed fully.
Fixed a robot removing from backsides bug

Robot's the copied and added weren't removing temporary copies from the
backside widgets so they appeared when refreshed.