WIP action back in controller.
WIP this seems to be the right way to disable

However, it also throws nil errors when &this doesn't exist yet.
Working(?) AnimationPane form

[#52818341] This enables/disables the x-min and x-max fields depending on the animation. There are some visual updates needed: the fields should be better labeled and there should be a better visual indication that the fields are disabled.

Still there's a problem saving the pane's page association.

https://www.pivotaltracker.com/story/show/52818341