Implement DELETE /x/purge

Implement x/purge which hard deletes x from the database.

Add the 'defaultClock' helper value.

Signed-off-by: Alexander Berntsen <alexander@plaimi.net>
Signed-off-by: Stian Ellingsen <stian@plaimi.net>
Reviewed-by: Stian Ellingsen <stian@plaimi.net>