Bootstrap4: Duplicate requests when opening modal windows

[irtimir]

I found a problem when opening modal windows. When using bootstrap 4, if you open a detailed view (creation and editing too) on the list page, then each subsequent request will be duplicated relative to the previous one, this happens due to the repeated loading of bs4_modal.js, in the case of bootstrap 4 this is not necessary, since the bs4_modal.js and details_filter.js scripts already loaded in list.html template.

Minimal example: https://github.com/irtimir/flask-admin-bs4-modal-issue