Preserve and display historical data

[nilmerg]

The Certificate Usage view currently lists known and recently seen hosts.

Issues:
a) Known but recently missing hosts are hidden.
b) Every registered host has only a single (latest) certificate chain. Though, there may still be multiple chains from the past which are currently hidden.

Solutions:
a) Recently missing hosts are shown, either by arranging them at the very end of the list or by displaying them with a quick filter.
b) Hosts get a history section which shows all previously known certificate chains.

[widhalmt]

Please add an option to remove historical data if it's not needed anymore. Some users get confused by overload of data and there should be an option to manually remove historical data that's not needed anymore.