XMPP and LDAP cleanup
Here's a summary of the major changes:
- When creating an LDAP user, or changing their password, the new password is sent to the action using stdin, instead of a command-line option.
- LDAP authentication for XMPP is enabled in the on_install setup. The option to disable it has been removed.
- The XMPP user registration form is removed.
- Removed in-band registration option for XMPP. It doesn't work with LDAP authentication. (I think we could substitute this feature with an option to allow guest users to register non-admin accounts through Plinth.)
- Add option to enable/disable the XMPP service.