Unify DefaultViewConfiguration & AdminViewConfiguration

[jstriebel]

Detailed Description

When retrieving the dataset info via /api/datasets/<orga>/<ds>, the view configuration that is edited from the webknossos frontend is shown in the key adminViewConfiguration (e.g. here). However, uploaded datasets and datasets in the datastore use the key defaultViewConfiguration. When applying those in the frontend, it uses the merged version of those two (see here for related backend code). I assume the separation of default and admin view configuration should rather be an implementation detail, which should not be exposed via the dataset info request, which should just include the merged configs as the default view configuration instead. We might also reconsider why those two are stored separately, and how this might be avoided completely.

related issue in wk-libs: https://github.com/scalableminds/webknossos-libs/issues/604, cc @philippotto