Chown log/pid on startup.

Refs #5787
Documentation: Fix StateFilterOK for recovery notifications.

Refs #5762
icinga2-{disable,enable}-feature should check if "ln" worked.

Fixes #5753
Empty command string on CHANGE_{HOST,SERVICE}_EVENTHANDLER should disable event handlers.

Fixes #5670
Documentation: Add note on dependencies and inherits parents.

Fixes #5742
Documentation: Split 'advanced' into multiple sections.

Fixes #5791
Implement == and != operators for AExpressions.

Refs #5789
Implement support for local variables in AExpressions.

Refs #5789
Implement the 'apply template' directive.

Refs #5789