Adding output_parameters to the Session

[XX-Yin]

Is your feature request related to a problem? Please describe.
Move my personal discussion with @saskiad to here.

The flexible output_parameters only existed in the StimulusEpoch, which does not make sense. A lot of parameters are related to that session instead of a specific stimulus. We should also add the output_parameters to session.py/Session.

Describe the solution you'd like
A clear and concise description of what you want to happen.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[dbirman]

This is very old, but in any case this is now covered by the Code objects