[Draft] Various fixes for Bayesian Linear Regression

[vandenman]

[ in progress, will be updated over time, pr is just open to run the tests]

• Improve QML to have separate double fields for each prior, so they can be documented separately and have saner defaults and bounds.
• Add footnotes to summary table and plots to explain that the model averaged credible intervals are computed while including models that assume the effect is absent.

[github-actions]

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