Individual block expand/collapse buttons nonfunctional

[zerocrates]

https://forum.omeka.org/t/exhibitbuilder-expand-collapse-issue/15044

I imagine this is a regression from the new 3.0 admin theme.

[zerocrates]

@kimisgold looks like this was caused by 8d04af6: you reworked the options sections to work on a class but the same expander/collapser is used for the whole block as well.

[kimisgold]

This should now be addressed in 192a122.

[zerocrates]

Fix finalized in 841bd93