read password from config file instead of generating one new every time

Add role prefix to role specifig variable to avoid conflicts when
using multiples role on the same machine on the same play.

- User last official deb package from matrix.org

- Revised LDAP integration:
  * ldap_server, ldap_domain [ ldap_basedn ] config vraiables.
  * Bind a protected service account with a service password and
    start-tls

- Hardcoded matrix.lilik.it --> {{ ansible_hostname }}.{{ domain }}

- Sqlite -> Postgres

New variables:

- matrix_domain | default($domain)