Make hide/unhide parameters clearer

[gwhitney]

Aaron points out that it's a bit unclear that some checkboxes are just going to control parameter visibility. It would be good to have them rendered as "dropdown rectangles", and possibly have distinctive typography, and/or used displayed names like "Show animation controls" instead of just "Animation controls".

[katestange]

This also came up in my brother's playing with Numberscope (#510 (comment)). I think there are two semantically distinct things we are currently using the checkboxes for: (1) show more parameters (2) activate/toggle a behaviour. I think these should be de-coupled. We discussed having a toggle switch like for list/thumbnail view when it is activating a behaviour, and a dropdown arrow for hidden parameters.