Refresh queries

Currently, first access to the data of a query starts a Job on the server, which is referenced by all further access. The job will eventually expire (this is a server setting, with possibility of being overridden when starting the job). We should save the expiry time of the Job when creating it, and refresh when it has expired. This will not give realtime queries, but periodically updating ones.
Currently, using an expired Job causes a hard-to-understand error, and the only way to correct is to re-instantiate the source object.