Builds no longer depend on a preexisting config in ~/.ssh.

sessioninfo integration for sessionimport

This MR refactors the import of the public pool attributes for sessions.

See merge request !25

Convert database user IDs to lowercase on account creation an login.
Additionally, LDAP UIDs are lowercased as a fallback when they cannot be
retrieved from the server.

Fixes failing start up because of no longer existent
`security.guest.lecturer.enabled` setting.