Speed up config compiler.

Fixes #5255
Fix leak in the config parser.

Refs #4946
Implement support for making script variables constant.

Refs #4946
Remove Windows example config.

Refs #4946
Implement support for constants in the config parser.

Refs #4946
Fix: display_name property doesn't work for hosts.

Fixes #5258
Merge branch 'feature/constants-4946' into next

Fixes #4946
Debian: Made handling of features-enabled respecting disabled features.

The default features now only get enabled on fresh installs. This has been
changed for icinga2-common and icinga2-classicui.

Fixes #5102
Debian: Fixed config check and changed DAEMON_ARGS in init script.

Check now actually works, command was incorrect and not properly blocking the
actual action on fail.

Also the config file is now in DAEMON_CONFIG variable.

Fixes #5086
Debian: Made creation of icinga-version.h.fallback safer.

We now use a custom CMakeLists.txt to just create this file without checking
dependencies or doing other stuff.

Idea is to avoid breaking on systems that only create source packages for
chroot builds.

Refs #5261
Make ICINGA2_{USER,GROUP,COMMAND_USER,COMMAND_GROUP} variables overwritable.

Fixes #5257
Add unit test for Stream::ReadLine.

Fixes #5077
Make status.dat/objects.cache interval configurable.

Fixes #5262
Set rlimits in the Application class (rather than in the init script).

Fixes #5260
DB IDO: Fix reconnect config/status inserts.

Fixes #5266
Make sure that TimePeriod segments are being merged properly.

Refs #5268
Rename one of the example timeperiods.

Refs #5268
Merge branch 'feature/timeperiod-fixes-5268' into next

Fixes #5268
RPM: Don't re-enable disabled features on update, proper remove on uninstall.

Fixes #5267
Implement scheduled downtimes.

Fixes #3584