fix form_elements dropdow menu (deselect all)

Summary

This MR provides a fix for #212 (closed) (supposedly) and another AWI bug (caosdb/customers/glaz_awi/management#210).

Focus

Apparently, the API of bootstrap-select changed since 1.13.9 (which we were using prior to the bootstrap-5 update) or we didn't use the documented API to achieve what we were doing.

Now, the relevant code for clicking the deselect button in form_element.js is up-to-date.

Also, I updated to a stable bootstrap 5 release and made some adjustments to styling of rows in the forms generated by form_elements while I was at it.

Test Environment

• please test this with AWI

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