Fix issues with the group sync with "Replace" strategy

[wynnset]

Fix issues with the group sync when choosing "Replace group rather than merge" flag

• Update both import and export logic and also do some refactoring
• For import, ensure Canvas group is seen as empty if it contains only ineligible members (i.e. members not in iPeer)
• For import, fix an issue with merging the imported non-empty groups with imported empty groups
• For export, if update flag is on, delete all the groups in canvas right away to allow users that are in other groups to be exported (if in only 1 iPeer group)
• For export, check group memberships when exporting each group (mainly code refactoring)
• Fix an issue when sync was not working as expected when group names are numeric
• Improve error messages

Closes: #556

[wynnset]

@kitsook good call. I added in a check for that and it lets the user know they need to change their Canvas groups to have unique names before being able to sync (disables sync meanwhile).

[wynnset]

@xcompass this is ready to be merged in. Feel free to either merge it in or let me know if you'd like me to make any other changes.