Set up LDAP management application

In case the LDAP directory service installed with #16 doesn't have its own management UI, this ticket:

LDAP management must be a web UI which allows editing LDAP registries (DNs, RDNs, roles, groups etc)
sets up an LDAP management application in its own docker container
starts that container as a service in docker-compose.yml
connect LDAP management to the LDAP registry from #16 so that it can manage roles, groups etc
modify nginx so that LDAP management is accessible under ldap.cnvc
any persistent volumes should be mapped and/or a database (reuse postgres/redis or setup new db container) should be used

ggeorgovassilis / codename-vincent