[INTERNAL] cleaned up MucNeg.Manager class

Made remaining protected fields private and added final keywords.

Change-Id: I048232820e78ff8ee4361164c42612a724bb0325
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1805
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>