Payments add modal form

* 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

user/templates/user/notifications.html

@@ -1,5 +1,5 @@
 {% extends 'base.html' %}
 
 {% block body %}
-    {% include 'generic_table_form.html' %}
+    {% include 'table/generic_table_form.html' %}
 {% endblock %}