Minor enhancements

* refactors eco account rest surface calculation into designated method get_available_rest()
* refactors placeholder setter for BaseForm
* adds automatic eco account identifier generating on saving
* fixes ServerMessageImportance template tag

compensation/tables.py

@@ -238,10 +238,7 @@ class EcoAccountTable(BaseTable):
         Returns:
 
         """
-        withdraws = record.withdraws.all()
-        withdraw_surfaces = withdraws.aggregate(Sum("surface"))["surface__sum"] or 0
-        after_states_surfaces = record.after_states.all().aggregate(Sum("surface"))["surface__sum"] or withdraw_surfaces ## no division by zero
-        value = int(((after_states_surfaces - withdraw_surfaces) / after_states_surfaces) * 100)
+        value = record.get_available_rest(as_percentage=True)
         html = render_to_string("konova/custom_widgets/progressbar.html", {"value": value})
         return format_html(html)