[NbtkExpander] animate the allocation
[NbtkExpander] animate the allocation

Animate the allocation rather than forcing fixed size changes.

pwithnall/mx,clutter-project/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx