Make ophys analysis functions robust to lack of cell_specimen_id

[matchings]

Experiments that are not part of an ophys container or do not have cell matching run on them for whatever reason will not have values for cell_specimen_id (they will be NaN). This breaks several functions that expect the cell_specimen_id column, including build_tidy_cell_df.

We need to add some functionality either defaults to use cell_roi_id when cell_specimen_id is not present, or replaces the values of cell_specimen_id column with the values of cell_roi_id to ensure that subsequent functions can run.

The former solution is probably preferable in terms of explicitness (i.e. you know for sure that cell_roi_id was used, but likely requires more extensive intervention into the code.