* adds modal form for adding payments
* generalizes generic_table_form.html for table-form-like usage in modal_form.html
* adds css enhancements for focused input fields
* adds BaseModalForm as specification to BaseForm, which inherits the BSModalForm class as well
* adds translations
* adds related object overview in detail view
* adds comment field to payment model for 'Verwendungszweck'
* simplifies intervention urls
* adds translations
* adds user access relation to certain models
* adds pagination to tables
* adds checked_on/_by attributes to intervention model
* adds custom column rendering for checked and registered columns
* adds first simple index filtering of default interventions for user
* adds translations
* No detailed permissions due to django constraints on model-based permissions
* instead: logic controlled permission by group membership
* adds translations