v6.0-beta.15

* Issue **#966** : Proxy was always reporting zero bytes for the request content in the receive log.

* Issue **#938** : Fixed an NPE in authentication session state.

* Change the proxy yaml configuration for the stack to add `remotedn` and `remotecertexpiry` headers to the receive log

* Change logback archived logs to be gzip compressed for stroom and proxy

* Uplift stroom-logs content pack to v2.0-alpha.3

* Uplift send_to_stroom script to v1.8.1

* Issue **#324** : Changed XML serialisation so that forbidden XML characters U+FFFE and U+FFFF are not written. Note that these characters are not even allowed as character references so they are ignored entirely.

* Issue **#945** : More changes to fix some visualisations only showing 10 data points.