split plugin dirs, created new cleaner import path for plugin config in settings.py

archivebox/extractor_plugins/singlefile/models.py

@@ -0,0 +1,14 @@
+from django.db import models
+
+from core.models import ArchiveResult
+
+class SinglefileResultManager(models.Manager):
+    def get_queryset(self):
+        return super().get_queryset().filter(extractor='singlefile')
+
+
+class SinglefileResult(ArchiveResult):
+    objects = SinglefileResultManager()
+
+    class Meta:
+        proxy = True