restructure instance settings

This moves around some checkboxes in the instances. As this is a bit messy I split it into multiple commits.

There are two important bits:

-  `instance.allow_thumbnailbadges` is deprecated and should always be true
-  the ui for configuring final adoption votes was removed

As this is part of #665 I am not sure if we should merge this now into develop. It would be better if we could synchronize all parts of that task.