OPENDJ-902 (CR-1654) Add connectionID to the HTTP access log + move to extended log format

HTTPConnectionHandler.java, HTTPClientConnection.java, CollectClientConnectionsFilter.java, SdkConnectionAdapter.java:
Added support for statistics.

02-config.ldif, config.ldif, HTTPConnectionHandlerConfiguration.xml, HTTPConnectionHandlerCfgDefn.properties:
Added "keep-stats" property.

02-config.ldif:
Added attributes "ds-mon-http-*" for monitoring HTTP statistics.

LDAPStatistics.java:
Changed getMonitorData() return type to List.
Made createAttribute protected.

HTTPStatsProbe.java, HTTPStatistics.java: ADDED