The previous method of hardcoded filepaths, specifically for events
belonging to core, meant that any events belongs to core subsystems
were omitted (core_customfield, core_h5p, core_payment, etc).
This patch adds two new functions to the event base to allow deprecation of
the individual events, without entirely removing them from the UI.
This is different to our normal deprecation procedure because all events
must support display of historical data. It must also be possible to view
the event information in the event monitor.
Paul Holden