Don't pass user list to tasks in newsletter

[ihucos]

We should not work with lists of ids but with the lazy evaluated querysets. So we need a solution where users are not passed one by one in a list to the tasks, the queryset should be generated inside task or the queryset should be serialized and passed to the task as a queryset.

This issue is a nicer version of https://github.com/liqd/a4-meinberlin/issues/1387

[fuzzylogic2000]

@rmader We are still doing that, but were not convinced that we shouldn't. What's your opinion? Should we change it or close the issue? Also, if we change it, that would mean a task for every email? That seems excessive!

[rmader]

The general idea sounds reasonable to me but to quote from #1387:

So this seems not to be really a scaling problem, but something about good practice.

So if this ever becomes a problem we should indeed look into it. Maybe low prio label or simply close :/