Initial Provenance State

[keckelt]

Add an initial state to the provenance that saves the notebook as loaded. I.e., either

• empty (for new notebooks), or
• with the cells that already existed in the notebook when loading it in an environment with loops.

This should avoid having all new cells in the first state if an exisiting notebook is loaded. and you can see when the analysis process started (and note just when the first aggregated state ended).