feat(core): Add custom exception class

ref: #248 #373

app/core/exceptions.py

@@ -1,5 +1,20 @@
+from rest_framework import exceptions, status
+from rest_framework.exceptions import (
+    ValidationError,
+    PermissionDenied
+)
 
 class MissingAttribute(Exception):
     """ An attribute is missing"""
 
-    pass
+    pass
+
+class APIError(
+    exceptions.APIException
+):
+
+    status_code = status.HTTP_400_BAD_REQUEST
+
+    default_detail = 'An unknown ERROR occured'
+
+    default_code = 'unknown_error'