refs https://github.com/TryGhost/Ghost/issues/12602
In order to build up a list of un/subscribes over time we have to use
the customQuery functionality to run SQL aggregates - this is "hidden"
behind an option, so that we can find{All,Page} as usual.
refs https://github.com/TryGhost/Ghost/issues/12602
Member Events in general are read-only after they've been created, so
we've explicitly disallowed destroying and editing via the model