Issues with initial fetch of user groups

When I was reviewing #310 (closed) I found that system groups are not properly fetched by the UI. When I entered the users view, the drop down that normally allows for selecting which group the new user should belong to was empty. Also, the non admin user had 'unknown' group assigned in the users list. It seems there was a race between services in getting the list of groups.

The viable solution seems to be to move the initialization of the groups to the ServerDataService.