Implement notification to plugins for disconnect request, connect, drop,
and close. This allows plugins to properly handle slaves and the master
server shutting down without sending messages that will get lost.
Fix research_sync sending out contribution events for the previous level
of a researched technology and sending finished events for the wrong
level when synchronizing technologies. Both of these issues are related
to failing to accunt for the unlocked level being one less than the
level stored when the researched property is false.
Hornwitser