Compensation control

* removes CompensationControl model
* adds comment field to CompensationAction
* adds max length of 200 for comment fields in forms
* adds rendering of error messages in case of invalid form input
* adds/updates translations

compensation/templates/compensation/detail/includes/states-after.html

@@ -23,7 +23,7 @@
     <div class="card-body scroll-300">
         {% if sum_before_states > sum_after_states %}
             <div class="row alert alert-danger">
-                {% trans 'Missing surfaces: ' %}{{ diff_states|floatformat:2 }} m²
+                {% trans 'Missing surfaces according to states before: ' %}{{ diff_states|floatformat:2 }} m²
             </div>
         {% endif %}
         <table class="table table-hover">