Refactoring

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

compensation/models/state.py

@@ -0,0 +1,36 @@
+"""
+Author: Michel Peltriaux
+Organization: Struktur- und Genehmigungsdirektion Nord, Rhineland-Palatinate, Germany
+Contact: michel.peltriaux@sgdnord.rlp.de
+Created on: 16.11.21
+
+"""
+from django.db import models
+
+from codelist.models import KonovaCode
+from codelist.settings import CODELIST_BIOTOPES_ID
+from compensation.managers import CompensationStateManager
+from konova.models import UuidModel
+
+
+class CompensationState(UuidModel):
+    """
+    Compensations must define the state of an area before and after the compensation.
+    """
+    biotope_type = models.ForeignKey(
+        KonovaCode,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        limit_choices_to={
+            "code_lists__in": [CODELIST_BIOTOPES_ID],
+            "is_selectable": True,
+            "is_archived": False,
+        }
+    )
+    surface = models.FloatField()
+
+    objects = CompensationStateManager()
+
+    def __str__(self):
+        return "{} | {} m²".format(self.biotope_type, self.surface)