user-related operations

[magdziarek]

When a user deregisters from CAS BioCollect doesn't clear any data connected to the user. No personal data is stored and the observations have to be kept, however:

• when project page is opened in the admin tab, members, if the members deregister from CAS, DataTables returns an error because the name can't be found in the authentication service - this s because userPermissions are not clean
• to be consistent maybe we should also remove the userId from person collection (person.userId)

Potential solution:

• periodically check the authentication system for which users don't exist anymore and remove their records from userPermissions collection, unlink their userId from personCollection