CASC-220: Support front channel SLO logout

First commit
CASC-220: Support front channel SLO logout

specific front logout parameter + Tomcat valves update
Merge remote-tracking branch 'upstream/master' into CASC-220
CASC-220: Support front channel SLO logout

Updates after Misagh's code review
CASC-220: Support front channel SLO logout

Update after Scott's code review
CASC-220: Support front channel SLO logout

Updates after Marvin's code review
CASC-220: Support front channel SLO logout

Update after new Misagh's comments
Merge pull request #68 from leleuj/CASC-220

CASC-220: Support front channel SLO logout