Refactoring

* splits compensation/models.py into subpackage
* renames base objects by adding suffix Mixin

compensation/models/payment.py

@@ -0,0 +1,38 @@
+"""
+Author: Michel Peltriaux
+Organization: Struktur- und Genehmigungsdirektion Nord, Rhineland-Palatinate, Germany
+Contact: michel.peltriaux@sgdnord.rlp.de
+Created on: 16.11.21
+
+"""
+from django.core.validators import MinValueValidator
+from django.db import models
+
+from intervention.models import Intervention
+from konova.models import BaseResource
+
+
+class Payment(BaseResource):
+    """
+    Holds data on a payment for an intervention (alternative to a classic compensation)
+    """
+    amount = models.FloatField(validators=[MinValueValidator(limit_value=0.00)])
+    due_on = models.DateField(null=True, blank=True)
+    comment = models.TextField(
+        null=True,
+        blank=True,
+        help_text="Refers to german money transfer 'Verwendungszweck'",
+    )
+    intervention = models.ForeignKey(
+        Intervention,
+        null=True,
+        blank=True,
+        on_delete=models.CASCADE,
+        related_name='payments'
+    )
+
+    class Meta:
+        ordering = [
+            "-amount",
+        ]
+