[FEATURE] Allow anonymous logging

    New options in config allow the anonymized storage of statistic log
    informations.
    (necessary e.g. in Germany: see e.g. http://www.saechsdsb.de/ipmask)

    config.stat_IP_anonymize:
      set to 1 to activate anonymized logging
    config.stat_IP_anonymize_mask_ipv4:
    config.stat_IP_anonymize_mask_ipv6:
      Prefix-mask (0..32 for IPv4, 0..128 for IPv6) to use for
      anonymisation. Setting this to will log an empty hostname.
      Recommendation for Germany: config.stat_IP_anonymize_ipv4 = 24
      if not set, defaults to 24  and 64, resp.

    config.stat_logUser: configure username logging

    CGL-cleanup in statistics function.

Change-Id: Id03841ad19343b7b6820d780d0769154c5a880b0
Resolves: #25404
Releases: 4.7
Reviewed-on: http://review.typo3.org/1289
Reviewed-by: Stefan Neufeind
Reviewed-by: Dominik Mathern
Tested-by: Dominik Mathern
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter