Implemented quite a few fixes to Personode GUI. Not limited to:
- Using radio buttons where warranted instead of checkboxes
- Fixing some instances where not selecting images or other parameters or returning empty selections would freeze or glitch the GUI
- Added requirements for both SPM12 and MarsBar; bundling 'marsbar-0.44.zip' (GNU GPL licensed) with the library
- Added a step-by-step example (with pictures!) and also a brief introduction to the toolbox
- Hiding the GUI when it's not interactive