Migrations + Cleanup

* adds needed migrations
* refactors forms.py (700+ lines) in main konova app
    * splits into forms/ and forms/modals and single class/topic-files for better maintainability and overview
* fixes bug in main konova app migration which could occur if a certain compensation migration did not run before

konova/models/object.py

@@ -749,7 +749,6 @@ class GeoReferencedMixin(models.Model):
 class ResubmitableObjectMixin(models.Model):
     resubmissions = models.ManyToManyField(
         "konova.Resubmission",
-        null=True,
         blank=True,
         related_name="+",
     )