...when node_id exists in the DB

Warning: this silently avoids insertion of patches when node_id is
missing for some reason in the history.

We had a conflict here: archive history is used to resolve new
patches. However, they were saved with delay and after that were
cleared. We should save archive immediately and immediately clear it
in mvar so it's ready for new patches.

Updates weren't calculated properly.

Previously, we have different version for different rows in one node.

This is used to save when quitting the server. Previous, debounce
save, didn't work properly on exit.

This is so that we correctly order _a_history later.

This doesn't work with locks yet.

Read in backend works now, insert and upsert not yet.

Also, fix bug with reversing the history.

This is not the optimal solution since it duplicates so much
data. Best would be to add "children" in the node directly.