Model state branching / merging

Created by: fg-uulm

Allow users to work on a separate "copy" of the dataset privately. There are different scenarios for that:

1. Saving/recalling a snapshot of the dataset state (global and local)
2. Private mode (branch from global, modify, then either discard or make global)
3. True instancing (second "private" dataset visualization, but also visible to other users)