The connection handling and code isn't really good, but not
really actively maintained either.
Besides that, the "telnet" method doesn't allow for TLS,
this needs a general rewrite against their HTTP API.
I've also added function documentation where applicable.
This patch ensures that specific configuration types
are pre-activated and post-activated. In general,
logging is first, then common configuration objects
like host/service, downtimes, etc.
In the end, all features are activated after to ensure
that notifications are only sent once downtimes are applied.
A similar thing happens for starting with checks too early.
The ApiListener feature runs first to allow cluster connections
at first glance.
fixes#6057fixes#6231