task -> shared_task (#21)

* task -> shared_task

fixes #20

* keep current flow, but implement fallback to shared_task

* revert change

Author: Jens Timmerman

task_api/backends/celery.py

@@ -2,7 +2,7 @@
 
 import json
 
-from celery import task
+from celery import shared_task
 
 from task_api.backends.base import TaskBackend
 from task_api.models import TaskInfo
@@ -13,8 +13,7 @@ def run_task(self, info, class_str):
         result = execute.delay(info.pk, class_str)
         info.backend_data = json.dumps({'celery_id': result.id})
 
-
-@task
+@shared_task
 def execute(task_id, class_str):
     info = TaskInfo.objects.get(pk=task_id)
     cls = CeleryBackend().resolve_class(class_str)