ZON-3409: Rewrite `PublishTask` and `RetractTask` to act as `celery` tasks.
ZON-3409: Rewrite `PublishTask` and `RetractTask` to act as `celery` tasks.

- a celery task *must not* have a `__call__` method, since defining classes as
  tasks only works via inheritance, which means that the `__call__` of the
  actual task is overwritten

- the actual work must be performed in the `run` method, which is called by the
  celery task (therefore we had to rename existing `run` methods)

- change the signature of `run` (previously `__call__`) to only accept an
  `uniqueId`, since celery tasks are serialized via json

- cleanup `lovely.remotetask` artifacts

ZeitOnline/zeit.cms,ZeitOnline/zeit.cms,ZeitOnline/zeit.cms,ZeitOnline/zeit.cms