remoting: multicast messages into debug log
icinga2.conf.dist: add CompatLog as default
Compat: log notifications (wip)

- we need a way to figure out which last commend id (or, author and
  text) where set when type is CUSTOM or ACKNOWLEDGEMENT
- GetCheckCommandName was required too
- not sure if notifications.cpp is the correct location

refs #4361
refs #3985
refs #2750
Merge remote-tracking branch 'icinga2/master'