Responds to #218

Main updates:

• adds settings to a saved out FOOOFGroup report
• adds the option to choose whether settings are saved for saving out both FOOOF and FOOOFGroup reports
• tweaks some sizing to make the reports work / look good
• adds the option to pass in explicit figure sizes for model plots

Note: for review, the code changes here are fairly simple - but it would be useful to check that when running the report generation code locally, that the sizing and layout looks alright!