previously used app.jf.CacheExpiry = time.Now(), now either call
app.InvalidateJellyfinCache() (when we only need it to get a user),
or app.InvalidateUserCaches() (when the web user list needs to be
updated).
jellyseerr already did this, but it's been standardised a little more.
Mediabrowser uses it's own genericErr function and error types due to
being a separate package, while jellyseerr and ombi now share errors
defined in common/.
Much like activities, you can have an expired account disabled, then
deleted after n days (unless the admin intervenes and re-enables the
account).
For #341.
Harvey Tindall