Make "DailyArtworkUpdates" a global option

This makes the DailyArtworkUpdates setting a global setting so it can be
properly configured on any frontend. This patch does not include any
code to fix an existing improperly configured setting, which could cause
problems in the future, as the per-host option will override the global
one and will be uneditable without direct database modification.

Refs #12033
(cherry picked from commit ffa364019e7d5bc0b88f4c83d21511090735b45d)