OPENDJ-830 (CR-1538) Implement authentication and authorization for HTTP connection handler

Added the possibility for the HTTP Connection Handler to accept unauthenticated requests.

CollectClientConnectionsFilter.java:
Extracted method getAuthenticationInfo() and added support for unauthenticated requests here.

CollectClientConnectionsFilterTest.java:
Added tests.

HTTPConnectionHandler.java:
Added acceptUnauthenticatedRequests().

config.ldif, 02-config.ldif, HTTPConnectionHandlerConfiguration.xml, HTTPConnectionHandlerCfgDefn.properties:
Added property 'ds-cfg-authentication-required' with default 'true' to HTTP Connection Handler