MyController/MyView: Complete Export functionality. 
- Completed the Hierarchy saving feature. 
- Added code to catch empty arrays, and throw error messags. 
- Rename 'saveCSV' to 'roleDataCSV' as this method will only handle the
role data. 
- Rename 'writeStringToFile' to 'SaveStringAs' and moved the file
chooser into this method. 
- Enable 'Export > Hierarchy', setup action commands.
MyController: Tweaked error message text.
MyController: Additional comments.