Akonadi Control: clean-up retired resources on start

When during start, Akonadi Control finds configuration for resources whose agent types are missing (they are no longer installed) and are present on a list of retired agent types, it can safely forget about them and remove all their left-over data from Akonadi.

The list contains resources that we are planning to retire in the near future. When users fail to migrate away from them manually and update to a new version of Akonadi that will no longer have those resources, they would be forever stuck with their Collections and Items in the database with no easy way to remove them. This code will take care of cleaning up the mess for them.

We have an explicit list of retired agent types, so that we don't accidentally wipe data of still-living resources in case the user installation gets corrupted, there's a packaging bug that causes the resource to be missing from the package and other even more unlikely scenarios...but it's better to be careful in this case.