Keep deleted Hosts and Services

[mwaldmueller]

Keep deleted Hosts and Services in the database. Especially for Reporting it's often necessary to have statistics for the past.
Of course it would be nice to have a cleanup option, so that they can be deleted after some time. It's not a nice workaround to keep orphaned Hosts and Services in the monitoring just to show them in the reports.

Environment

Icinga: 2.14.2
Icinga DB: 1.1.1