Replace LDAP configuration

Replace modello based LDAP configuration with orient db

Acceptance Criteria:

• Make LDAP plugin stop use Modello (and have dropped use of it alltogether), and have it tied into "config" OrientDB instance.
• Module tests related changes as needed (as many of those "stuff" ldap.xml under tests), true for nexus-ldap-plugin module UTs as for nexus-ldap-plugin module ITs
• Remove use of Plexus from module UTs and ITs (as current tests were unmaintable, this was a desperate step of mine – cstamas)
• Update nexus-ldap-testsupport, remove Plexus (as use of the ldap testsupport module implied use of Plexus in dependant module, which is unwanted)
• Introduce nexus-ldap-client (needed to be able to manipulate LDAP configuration from "real" ITs, as copying ldap.xml does not work anymore)
• Update OSS legacy and modern ITs as needed (replace copied ldap.xml's with LDAP Rest Client use)
• Update Pro legacy and modern ITs as needed (replace copied ldap.xml's with LDAP Rest Client use)