Bug 33608: Redirect UpdateStats to Koha namespace

Bug 33608: Redirect UpdateStats to Koha namespace

Moving code to Koha::Statistic->new and ->insert.
Polishing code a bit further in next patch.

Test plan:
Run t/db_dependent/Stats.t
Run t/db_dependent/Koha/Statistics.t
Run t/db_dependent/Koha/Pseudonymization.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
[EDIT] POD headers, use plural module and tidy Koha::Statistic

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>