New states REPACKING/EXPORTED, new internal states, new maintenance runner for cleaning-up retrieve queue requests

Remove all the code associated to the activity weight fair share
scheduling feature:

- Remove catalogue functions interacting with the ACTIVITY_WEIGHTS table
- Remove code related to activity weights from the scheduler.
- Deprecate and mark as optional objectstore schema fields for activity
  weights (shcema should be backwards and forwards compatible).
- Store only activity information in the drive state. In the catalogue
  methods, default the weight values to 1.0 (avoids having to perform a
backwards incompatible catalogue upgrade)

And suppresses two false positive warnings in templated classes

Add youngestjobcreationtime to archive and retrieve queues in the
objectstore. The change is backwards compatible, as the new field is
optional and with a default value of 0.

The field is updated everywhere in the code where oldestjobcreationtime
is also updated. The value is printed per queue using cta-admin sq.

Using a dump tool and jq, the objectstore can be easily explored.
This README.md presents the methods.