server: add support for adding new users

Signed-off-by: Valentina Manea <valentina.manea.m@gmail.com>
server: add support for user listing

Signed-off-by: Valentina Manea <valentina.manea.m@gmail.com>
server: mark user as online on login

Signed-off-by: Valentina Manea <valentina.manea.m@gmail.com>