Role to configure nextcloud with LDAP User backend.

First test passed.

New modules:

- occ:
  set coniguration values using `php occ` nextcloud command-line tool.

Created a reusable tasks list for issung certificates (tls) at the
moment.

Added option for module cert_request to programmatically require
signing of client certificate.

Affected roles:

- gitlab
- nginx
- ldap

- Coherent quotation style
    Single quotes for text variable (even if implicit), no quotes for
    variable and conditional statements, if not required.

- Some useful tags added:
  * ssh_certs
	  renewal of server SSH certificates and configuration of authorized
      CA.
  * tls_pub
	  renewal of public TLS certificates (let's encrypt) and certbot
	  configuration.
  * tls_int
	  renewal of internal TLS certificates (service authorizations) and
	  configuration of authorized internal CA.
	  *(ToDo: deployment of Certificate Revokation Lists)*
  * lxc
      deployment of new containers (deployment of configuration file
	  excluded, for instance change in ip address are always applied and
	  trigger a container restart even if you skip this tag.
  * packages
	  installation and upgrade of software packages (apt, opkg or
	  tarballs)
  * service_password
     create new random password for services-only password, for routine
	 rotation. Not meant to be skipped (some roles need to know the
	 service password, so they do a rotation).

- prepare_host
- ssh_server
- lxc_guest
- ldap
- gitlab

- x509_subject_prefix
- x509_ldap_suffix
	*Replaces:* x509_suffix in ldap.yaml
- letsencrypt_email
	Used in roles/certbot and roles/gitlab
- root_ca_cert
	*Replaces:* ssl_ca_cert and files/lilik_x1.crt

New defaults:

- ldap_domain | default: `${domain}`
- server_fqdn | default: `${hostname}.dmz.${domain}`
	*Replaces:* fqdn_domain

Removed:

- fqdn_dmain
- x509_suffix
	*Replaced by:* x509_ldap_suffix in common

New defaults:

- server_fqdn | default: `${hostname}.${domain}`
   *Replaces*: fqdn
- ldap_domain | default: `${domain}`
- ldap_server | default: `ldap1.dmz.${domain}`
- ldap_basedn | default: `dn(${ldap_domain})`
- enable_https | default: `true`

New defaults:

- server_fqdn | default: `${hostname}.${domain}`

And minor improvements/refactoring

- Tasks splitted in subfiles.
- Static slapd configuration (slapd.conf) moved *properly* to dynamic
conf (slapd.d).
- TLS Enabled by default, with certificate acquired using
  `ca_manager`.
- New default tree
- New default ACL
- Kerberos schema added
- {SSHA512} hash properly configured.

Resolves #13