print message counts in statistics mode
benchmarking showed that the execution handler threads had no effect
bump graylog2-plugins version
make counters non blocking;

make periods of writes to mongo longer, because mongo hits CPU. made it simple by changing constant from 5 to 60 seconds.  for generic purpose it may be limited adaptively (by updates/sec) or just configured in .conf
(cherry picked from commit e23efcc0bdba3dc3c8818de900595074bbf25ec0)

Conflicts:

	pom.xml