Automatic maintenance of the ChecksumDatabase for the ReferencePillar

When the checksums of a file in the ChecksumDatabase is too old, it is recalculated.
Currently the this recalculation only happens when the checksum of the given file is requested.
Potentially this might cause the checksums of all the pillars to be recalculated at once, thus creating a large performance issue.

A scheduler with a workflow for continuously maintain the data in the ChecksumDatabase is needed for the ReferencePillar.