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

templates/table/generic_table_form_body.html

@@ -0,0 +1,20 @@
+{% load i18n %}
+        <table class="table">
+            <tbody>
+                {% for field in form %}
+                <tr title="{{ field.help_text }}" class="{% if field.errors %}error{% endif %}">
+                    <th scope="row" class="col-sm-3">
+                        <div>{{ field.label }}<span class="label-required">{% if field.field.required %}*{% endif %}</span></div>
+                        <small>{{ field.help_text }}</small>
+                    </th>
+                    <td class="col-sm-9">
+                        {{ field }}
+                        {% for error in field.errors %}
+                        <strong>{{ error }}</strong>
+                        {% endfor %}
+                    </td>
+                </tr>
+                {% endfor %}
+            </tbody>
+        </table>
+        <small>{% trans 'Fields with * are required.' %}</small>