plug-ins: uncomment animation-play in POTFILES.in
Another papercut on the way to fully translated menus.
animation-play was commented out in 662b7003 since it was a skipped plug-in.
It was however revived in 6bb03dc2, but not in POTFILES.in
This also removes it from POTFILES.skip, together with curve-bend which already was readded to POTFILES.in but not removed there.