Sync group memberships from LDAP
Currently, group membership for a user is imported from LDAP on first login. However, if groups are changed in LDAP later, they are never synced again into MyKDE, so we need to manually change membership in both places.
MyKDE should get groups from LDAP on every login to ensure the list is up to date.
(Note that this is obsolete once #19 is implemented, since then we would change group membership in MyKDE alone and let it sync to LDAP)