no issue
- member records are not re-fetched when navigating from the members list to the member details screen, instead the already loaded member object is passed through to the route directly to provide a faster navigation experience
- however, the objects used in the member list are proxy objects in order to support the lazy-loading infinite scroll. Proxy objects require the use of `get()` so errors were thrown when the newsletter subscription toggles were used
refs https://github.com/TryGhost/Team/issues/1492
Allows site owners to manage member's newsletter preference directly in Admin.
- also adds `visibility` property for newsletter model
- updates members test model to include `visibility`
