[Enhancement] Swappable Packages (#216)

Co-authored-by: Tim Lorsbach <tim@lorsba.ch>
Reviewed-on: enviPath/enviPy#216
Reviewed-by: liambrydon <lbry121@aucklanduni.ac.nz>
Reviewed-by: Tobias O <tobias.olenyi@envipath.com>

utilities/decorators.py

@@ -1,10 +1,12 @@
 # decorators.py
 from functools import wraps
 
+from django.conf import settings as s
 from django.shortcuts import get_object_or_404
 
 from epdb.logic import PackageManager
-from epdb.models import Package
+
+Package = s.GET_PACKAGE_MODEL()
 
 # Map HTTP methods to required permissions
 DEFAULT_METHOD_PERMISSIONS = {