Replace LDAP and Plinth user databases with systemd-homed.

Systemd-homed provides some additional features like:

• Encryption of home directories.
• Easier migration of user homes to another host.
• Ability to store additional data to a user profile (email, language, etc... ).
• More modern password hash method than in LDAP.
• Memory and disk quotas per user.

For more info visit https://systemd.io/HOME_DIRECTORY/.