Support for PEtab 2.0 #234

It would be great if PEtab-GUI would support PEtab 2.0, ideally, for now, in parallel to 1.0.

This will require quite a few changes (new tables, different object model, changed columns, no visualization table for now). Ideally, the model would operate directly on the underlying petab pydantic objects, not the dataframes. Updating the pydantic objects directly will provide more specific error messages.

To break that into more manageable chunks, one could start with only simple problems: SBML model, no mapping table, no experiment and condition table.