Update sesman to cope with separate authentication/authorization (AA) and
command processing.
Also, internally users are now tracked by UID rather thn username.
This addresses a problem found by some users using federated naming
services (e.g. Active Directory) where the same user can be referred to
in more than one way. See https://github.com/neutrinolabs/xrdp/issues/1823
The separation of AA in this way allows for multiple attempts to be made
on one connection to get a password right. This addresses MaxLoginRetry
not working (https://github.com/neutrinolabs/xrdp/issues/1739)