The integrity checker now depends on an abstract class that contains the
base code that is necessary to perform the check on a storage.
This abstract class can be inherited by concrete classes that will define
the checker behavior when a corrupted or missing content is find
(Note that for now, the checker runs on a local storage so the list of
content to check is made from walking the file system. So a missing
content shouldn't happens. But another version could get this list from
another source that is not the file system).
Also, add an checker that update archive database : this implementation
set the status of the archival database corresponding to the real state
of the object. This way, next archival scheduling, the storage may be
used as a destination for a file copy.