Edits the user guide and adds a Bayesian tutorial

[alexhroom]

This PR:

• edits the second chapter of the user guide for clarity
• uses the new Project.load() method to load the Python project data throughout
• adds the convert RasCAL python notebook
• and adds a tutorial explaining the specifics of doing a Bayesian analysis

[DrPaulSharp]

Thanks very much for taking this on. All looking good, I've a few points for you to consider.