Fix for issue #212 - Groups not reloaded when user is switched

See merge request !19

Fix for issue #209 - Issue does not update when label is added

- Trigger update for labels if necessary after updating issues
- Trigger update for notes after issue is edited (Required if assignee is changed while editing the issue)
- Use `notifyItemRangeChanged` instead of `notfiyDatasetChanged` for updating notes

See merge request !18

Fixed overlap in issue overview



See merge request !17

- Trigger update for labels if necessary after updating issues