Add PEtab export

[sebapersson]

Following parameter estimation it can be relevant to export the PEtab problem, which basically means to export a new parameters table. The exporter should fulfill:

• Exports the problem to a new folder for reproducibility.
• In case of SBML model exports the model file, in case of Catalyst or ODESystem model, exports a file which defines the model. Naturally this is not ideal, but given the package versions, this should be enough for reproducibility.