Remove any Object annotations

[philippotto]

Object is an alias for any and therefore quite bad for typing coverage. We should replace it by more precise types ({} comes closest to representing an actual Object with arbitrary keys).

I think, it's independent of #5338 since it strenghtens the typings in both type flavors.

[hotzenklotz]

As far as I can tell there is only one Object type remaining: https://github.com/scalableminds/webknossos/blob/master/frontend/javascripts/admin/admin_rest_api.ts#L2215

I guess we have significantly improved our typing game in the meantime :-) Consider fixing or closing the issue?