Variational Bayes algorithm with given noise

[TTitscher]

The current implementation always infers the noise. The option to not do that and instead provide a determinstic noise-sigma (as common in likelihood functions) is missing.

IMO this could be implemented by just skipping the update equations 21-22 (or 30-31 for multiple noises). Then, in the remaining update equations, the noise is only used as "scale x shape" which corresponds to the mean of this distribution, which could be provided instead.

Discussion:

• Are my thoughts correct?
• The free energy terms include the noise shape and noise scale separately. How to handle that?

[TTitscher]

We need other update equations!